HUMAN LACTATION

Lactation and reproduction *

A. M. THOMSON,1 F. E. HYTTEN,2 & A. E. BLACK 3

The authors review the literature on the effect of lactation on fertility in the absence of contraception and on the effects of contraceptive measures on lactation. They examine data from several countries on the intervals between births and on the return of menstru- ation and after childbirth, comparing lactating with nonlactating women. They conclude that lactation is an inefficient contraceptive for the individual, but that in popu- lations sustained lactation is associated with reduced fertility. Possible physiological mechanisms causing lactation amenorrhoea are discussed. Though much of the literature on the effect of contraceptives on lactation is inadequate, there is general agreement that the component of hormonal preparations has an adverse effect on lactation, but that progestins alone do not. Many questions remain. Is this effect seen in established lactation, or only in the puerperal period? Is it a direct pharmacological effect, or are pill-users the mothers least motivated to maintain breast-feeding? Does a close relationship exist between given and lactation performance? The authors comment on some ofthe technical deficiencies ofprevious studies in thisfield and discuss practicalpossibilities of, and limitations to, obtaining adequate scientific information in the future.

THE EFFECT OF LACTATION ON FERTILITY, enhanced and their sexual role as a female is height- IN THE ABSENCE OF CONTRACEPTION ened. We have far to go before we understand the function of post-partum taboos...". It is well established that a woman who is lactat- Return of fertility after a can be gauged ing is less likely to become pregnant than one who in various ways, with varying degrees of certainty. is not, and that the contraceptive efficiency of lac- (a) The only wholly certain evidence of fertility tation is imperfect. The reasons for this are by no is a further pregnancy, but the return of menstru- means simple. ation is generally accepted as indicating renewed As will be shown, lactation is accompanied by fertility. some delay in the return of fertility a following the birth of a child, but behavioural factors may be at (b) Menstruation has the great advantage of easy least as important as physiological factors. In some recognition, although for some weeks after delivery societies there are taboos against sexual intercourse there is the possibility of confusion with prolonged after parturition (1). Even in the absence of taboos, or renewed post-partum bleeding. But menstruation lactation may be accompanied by a spontaneous does not itself necessarily mean that ovulation has change in sexual activity. Raphael (2) says that occurred, and ovulation may precede the return of " some breast-feeding women have greatly lessened menstruation. sexual drives, while others find the act of lactating (c) The detection of ovulation is more difficult. so emotionally fulfilling that their femininity is Histological examination of the endometrium on the first day of menstruation is perhaps the most reliable * From the Medical Research Council Reproduction and field method available. Continuous measurement of Growth Unit, Princess Mary Maternity Hospital, Newcastle hormones excreted in the is more cumbersome upon Tyne, England. 1 Director. but almost as good. The field method most often 2Deputy Director. used has probably been the estimation of the rise ' Technical Officer. in basal body temperature, but this is only feasible a The term " fecundity " would be preferred to " fertility" with relatively well-educated women and is unreli- by demographers. We shall use " fertility " throughout this able, in women whose sleep is being review, in the belief that our meaning is clear from the particularly context. interrupted by the needs of children.

3358 - 337 BULL. WORLD HEALTH ORGAN., Vol. 52, 1975 338 A. M. THOMSON ET AL.

Child died Artificially fed Rwanda *~ - Child survived Ph lippines! * Breast fed 1-6 months Child died Breast fed 7-12months Nhigeri { Ch'ild survived - ----Breast fed 13months+ Eskimos f ----- Artificially fed 100 - ...... -Breast fed

O' 80 - 0. ., : A I I 60 -

I 40 - iI

20 -

12 24 36 48 12 24 48 Months between births

Fig. 1. Cumulative percentages of women giving birth to a child at different intervals after the birth of a previous child (for references see text).

Lactation and conception woman is taboo (5). The interval was shorter-about It is well known that a woman who is lactating 2 years on average-in Rwanda, where there was no is less likely to become pregnant than one who is such taboo (6). In nonlactating women of both not lactating, but reliable quantitative evidence is communities the average interval between pregnan- scarce. cies was only 1 year. Since pregnancy is caused by sexual Fig. 1 shows intervals between births from four intercourse, communities that were not using contraceptive de- it seems reasonable to suggest that the differences vices or drugs, and where prolonged breast-feeding between the communities illustrated in Fig. 1, and is usual. Among Filipino mothers who breast-fed also those between lactating and nonlactating women their babies for more than 6 months, about half in each community, may be explained as much by became pregnant within about 21/2 years; among the differences in sexual behaviour as by a biological much smaller groups who did not breast-feed at influence of lactation on fertility. Whatever the pre- all or who lactated for less than 6 months, the cor- cise influence of lactation, it is certainly an inefficient responding interval was about 2 years. In this com- means of contraception unless it is associated with munity, therefore, the effect of lactation in prolong- some reduction of sexual activity. In Egypt, Kamal ing infertility seems to be fairly small (3). et al. (7) gave pregnancy as the most important In the Eskimo women, occurred ear- cause of weaning in women of poor socioeconomic lier than among the Filipinos in both the lactating status: no less than 57 % of mothers attending a and the nonlactating groups, and the average inter- child health centre became pregnant while lactating. val between those two groups was longer-about Similarly, reports from the United Kingdom (8, 9), one year (4). USA (10), India (11), Mexico (12), and Senegal (13) In the two African communities, the nonlactating have emphasized that conception during lactation is women were those whose babies were stillborn or by no means unusual. died early. In a village in western Nigeria, the aver- Lactationi and menistruation age interval between pregnancies in lactating women was nearly 21/2 years. This is stated to be due to We can also study the problem by estimating the the fact that sexual intercourse with a lactating extent to which lactation postpones the return of LACTATION 339

Non -lactating_ Lactating- 100- .--- Italy (Bailo&Nobile) 100 - U S A. ,Salber) 90- 90 - U.K. (Crorin). -Taiwan (Join) .Bomboy (Baxi) Calcutta (Das&Mitra) 80- U.K. (Sharman) 80-

70- 70- Italy (Bai[o& Nobile) .S.A. (Salber) 60- 60 - U K. (Sharman)

50 - 50 - C- /1, 40 - 40 - / I* Bombay (Baxi) 30 - 30- // .'Toiwan (Jain) Punjab (Potter) ; ..:: _ & 20 - 20 - //..- Rwanda (Boute vanBaten) C eylon:::::~~Cylon (Chinnatomby)

10 - 10-

- X r X X X * X A 8 12 16 20 24 28 4 8 12 16 20 24 28

Weeks post-partum

Fig. 2. Cumulative percentages of women menstruating at different intervals after delivery, according to type of feeding. menstruation after a delivery. In this connexion, it is range from about 75% to 100%. Among lactating important to note that lactation is a physiological women, the corresponding range is much wider, function, whereas breast-feeding is a form of ma- from less than 20% (14) to more than 80% (15); ternal behaviour used to evoke lactation. Breast- there is an impression of two groups-one showing feeding behaviour can vary from frequent feeding that only 10-30% were menstruating by 6 months, at the demand of a vigorous and hungry baby that and the other that more than half had re-established receives as its only food to occasional menstruation by that time. At 3 months post use of the breast to feed a baby that receives partum, all reports except one show half the non- nourishment from other sources or is too weak to lactating women to have started menstruating. The suckle vigorously. Relationships between lactation apparently high incidence of returned menstruation and menstruation may therefore be influenced by in some groups of nonlactating women during the maternal breast-feeding behaviour. first 4-8 weeks post partum (50% or more) might In animals, estrus may be influenced by sexual possibly be exaggerated by confusion between true stimulation, or even by environmental factors, such menstruation and post-partum haemorrhage or with- as daylight. We cannot altogether dismiss the possi- drawal bleeding provoked by given to bility that similar influences may act on the human suppress lactation. reproductive cycle. At present, however, we do not The only general conclusion that seems permis- know of any evidence that the return of menstru- sible from the reports as a whole is that lactation is ation post partum is influenced by behavioural fac- usually associated with a considerable prolongation tors other than breast-feeding. of post-partum amenorrhoea, the duration of which Fig. 2 shows cumulative percentages of women seems to be highly variable, even when expressed who began to menstruate at various intervals after as group averages. Some of the variations may be delivery, in several different communities (6, 14, 15, due to technical inadequacies in the data, including 20, 22, 23, 29, 75, 76). Among nonlactating women, peculiarities of the samples of women studied. Very the proportions menstruating by 6 months (28 weeks) few of the reports give details of breast-feeding beha- 340 A. M. THOMSON ET AL. viour. As far as we can determine from the published Finally, the return of menstruation may be more evidence, all the women described in Fig. 2 as lac- rapid after abortion than after normal parturition; tating were in fact lactating when menstruation Baxi (11) found 65% and Potter et al. (22) 88% of started, but we cannot be absolutely certain. Some women to be menstruating one month after abortion. of the breast-fed babies no doubt received supple- mentary food, and information on the frequency Lactation and ovulation and strength of sucking is lacking. Differences in While the onset of menstruation can in general breast-feeding behaviour may have some bearing on terms be accepted as indicating the onset of ovulation the large variations in the incidence of menstruation and hence the return of fertility (24), there is a large among lactating women. Menstruation is said to amount of literature to testify that ovulation can return more quickly with partial than with full occur without menstruation and vice versa. That breast-feeding-for example, McKeown & Gibson (9) pregnancy can occur during lactation amenorrhoea found that, 4 months after delivery, the proportion is well known and widely documented (6, 7, 9, 10, of women menstruating was about 40 % in those 11, 27, 28). fully breast-feeding, 57 % in those partly breast-feed- Because of the techniques involved, studies of ing, and 95 % in those fully bottle-feeding. ovulation are usually made in better-educated women. The interpretation of comparative information is There is little or no direct evidence of the effect of further complicated by the fact that prolonged lactation on ovulation in ill-nourished populations. breast-feeding is frequently associated with a low In the nonlactating mother ovulation-like men- socioeconomic standard, and vice versa. Amenor- struation-tends to occur earlier than in the lactat- rhoea is undoubtedly common during famine (16) ing mother, and ovulation within the first month and poor-class lactating women may be severely after delivery has been reported. In Cronin's (29) undernourished (17, 18). Malkani & Mirchandani (19) series, investigated by recording basal body tem- found an inverse relationship between the length of perature, 2 of 90 nonlactating women ovulated amenorrhoea and family income; but Jain et al. (20) before 28 days, and Lamotte (28), in a study of found that maternal education and place of residence endometrial biopsies, found 4 out of 25 to have had no influence. Saxton & Serwadda (21) reported ovulated by 30 days, the earliest at 21 days post that amenorrhoea during lactation was longer, on partum. Lamotte (28) also showed that, when lac- average, among relatively well-nourished women in tation was suppressed by an estrogen/ Uganda than among Rwanda women " in a marginal mixture, ovulation was delayed; in 25 such cases nutritional state ". the earliest ovulation was at 36 days. Timonen & A number of studies show that the effect of lac- Lehto (30), who used a combination of urinary tation in delaying the return of menstruation is pregnandiol and vaginal cytology, found accentuated by rising maternal age (19, 22, 23). the earliest evidence of ovulation in 12 nonlactating Potter et al. (22), for example, showed that, of lactat- women to be at 43 days. Perez et al. (24) found an ing women aged 20-29, 31 % were menstruating at average of 49±12 days to ovulation in 30 women 6 months, compared with only 16% of women aged who had suppressed lactation ab initio by mechanical 30 years or more. That effect is denied by Jain and hormonal means. et al. (20), whereas Perez et al. (24) say that age In lactating women, the earliest ovulation found and parity had negligible effects-at least in the by Cronin (29) was 35 days post partum; Sharman absence of prolonged lactation. Maternal parity, (31) thought the earliest evidence of ovulation from apart from its relation to age, appears to have no biopsy material was about 6 weeks, and Timonen & independent effect on lactational amenorrhoea. There Lehto (30) found the earliest evidence of ovulation may be biological differences of an ethnic nature, and in 8 lactating women to be 60 days. Das & Mitra (15) even within ethnic groups the duration of lactational studied the vaginal cytology of 110 post-partum amenorrhoea may be to some extent an individual Bombay women and found evidence of ovulation trait, possibly genetic. Salber et al. (25) found that, in one at 27 days, but it is not clear whether this in women lactating after each of two successive preg- woman was lactating. nancies, there was a high correlation between the The most detailed study, so far, seems to be that duration of amenorrhoea during the two periods of of Perez et al. (24) in 200 lower-middle-class normal lactation, and El-Minawi & Foda (26) reported the obstetric patients of the Catholic University of Chile. same phenomenon in Egyptian women. Ovulation was diagnosed by " a battery of concur- LACTATION 341 rent tests including basal body temperature charts, first menses after suspended breast-feeding follow repeated observations of cervical mucus, timed va- ovulation in 90% of cases ". ginal cytology, and endometrial biopsies ". As already noted, 30 women suppressed lactation ab initio, Physiological basis oJ lactation amenorrhoea 16 suspended lactation within 15 days, and the It is widely believed by obstetricians that lactation remaining 154 lactated fully or partly for more than amenorrhoea is a period of ovarian inactivity; indeed 15 days. From life-table analyses, the investigators the phrase " physiological castration " has been concluded that 36% of fully breast-feeding women used. There is some clinical evidence. For example, ovulated by 18 weeks or earlier, but none before Keettel & Bradbury (33) say that in lactation there 8 weeks. Following full breast-feeding of unspe- is often atrophy of the vaginal epithelium sufficient cified duration, 65% ovulated within 18 weeks of to cause tenderness, and endometrial atrophy has changing to partial breast-feeding. After cessation been noted by a number of authors (26, 32, 34). of all breast-feeding of unspecified duration, 94% of The latter investigators gave evidence that the uterus women ovulated within 12 weeks. From the results itself is smaller than normal during lactation, with of regression analysis, the investigators suggest that a cavity shorter by about 0.5-1 cm. a lactation of 17.5 months or longer will prolong Reduced or absent production by the the absence of ovulation and/or amenorrhoea by ovaries during lactation amenorrhoea seems to have more than a year. However, since only 5 women been taken for granted or deduced from the evidence out of a sample of 200 breast-fed their babies for of vaginal cytology and endometrial patterns, but more than a year, and none for as long as 17.5 almost no direct information appears to have been months, this estimate of the average postponement published. The only convincing data come from the of fertility must be viewed with caution. Further- study of one individual by Brown (35), who showed more, since one-third of fully breast-feeding women that the urinary excretion of estrogens was consist- ovulated within about 4 months of parturition, the ently low throughout some 10 weeks of lactation, postponement is obviously highly unreliable as a rising to normal menstrual cycle levels after breast- means of avoiding pregnancy, from the point of feeding had been abandoned. view of the individual mother. On the other hand, The question whether the ovaries are themselves demographers and others whose concern is with in an unresponsive state, or whether the primary populations, are justified in asserting that sustained " failure " is pituitary, has not been satisfactorily lactation is associated with a considerable reduction answered. Timonen & Lehto (30), using a complex of average fertility. and subjective assessment based on vaginal cytology, concluded that " in the lactating woman there was Relation of ovulation to menstruation mostly a proper balance between ovarian function It has been widely believed that the first menstrual and secretion, but in the non-lactating period after pregnancy is usually anovular, and group 6 out of 12 exhibited ovarian insufficiency in some-but by no means all-studies support that the response to gonadotropin ". Keller (36) used belief. bioassay for pituitary gonadotrophins and found the Ovulation preceded the first menstrual bleeding in levels to be much the same as in menstruating only 12% of the cases studied by Das & Mitra (15), women; he thought that the lack of response by the 3 (15%) of the 20 women examined by Timonen & ovaries might be due to . A more elaborate Lehto (30), and 5 (14%) of 36 women studied by study by Keettel & Bradbury (33), by means of a Udesky (32). On the other hand, Cronin (29) found combination of bioassay for gonadotrophins and va- about one-third of his series of 171, and Lamotte (28) ginal cytology, concluded that there were three 23 of his group of 50, to have ovulated before the groups of women. " Type 1 is characterised by a first menstruation. continuous excretion of and a ten- There is a suggestion that a lower proportion of dency towards prolonged atrophic vaginal smears first cycles are fertile in lactating than in nonlactat- indicating low estrogen production due to temporar- ing mothers. According to Perez et al. (24), " re- ily refractory ovaries. Type 2 is characterised by sumption of menstruation during full breast-feeding intermittent excretion of gonadotropins and a rela- is preceded by ovulation less than half the time; tively early restoration of vaginal cornification indi- a first period during partial breast-feeding is pre- cating fairly responsive ovaries. Type 3 is charac- ceded by ovulation in almost 75% of cases; while terised by the absence of gonadotropins and varied 342 A. M. THOMSON ET AL.

vaginal epithelial patterns. This seems to represent who do not want to breast-feed, or in whom lac- a delayed recovery of pituitary function. With re- tation is contraindicated. Their efficacy has been sumption of pituitary activity, the ovaries are imme- debated (40) and their mode of action remains uncer- diately responsive." All three types occurred with tain. Experiments on animals have shown clearly equal frequency in both lactating and nonlactating that relatively high doses of estrogens do in fact women. suppress lactation; and, in the rat, milk secretion is Modern methods of assay should be inhibited even by low doses (41). With women who capable of clarifying this confused situation. are treated in order to suppress lactation the situ- Information now available on the mechanism for ation is complicated by the fact that suckling is releasing pituitary hormones suggests the possibility stopped, which theoretically may be as important that gonadotrophin release occurs reciprocally with as the direct influence of medication. Clinical experi- prolactin release, and makes sense of the fact that, ence indicates that, ifestrogens do have a suppressive whereas the gonadotrophins are released by their effect, it is present only while the hormone is being hypothalamic factors, prolactin release is inhibited taken. Reappearance of milk secretion may occur by its hypothalamic factor (37). If the three factors when the course of treatment ends. were all activated in response to a common mech- When contraceptive pills including estrogenic hor- anism-e.g., adrenergic tone-then the circumstances mones came into use, it was natural to consider that cause prolactin release would inhibit the gonado- whether there were any adverse effects on lactation. trophin-releasing factor and gonadotrophin would The literature has recently been reviewed by not be secreted, and vice versa. Evidence from the Chopra (42) in a widely accessible journal and rat (38) showed that suckling alone produced the need not be analysed here. Among the more recent effect, whether or not milk was produced, and clini- reports are those of Bhiraleus et al. (43), Borglin cal evidence further suggests that the hypothalamic & Sandholm (44), Casares Ponce (45), Chinna- mechanism works on a dose-response basis, since tamby (14), Gomez-Rogers et al. (46), Ibrahim & only full lactation, or continuous suckling, is effec- El-Tawil (47), Kaern (48), Kamal et al. (7), Koetsa- tive in suppressing ovulation (9). The effect is reduced wang et al. (49), Kora (50), Miller & Hughes (51), when even partial weaning is introduced. and Wallach et al. (52). Most of this literature is If that theory is confirmed, an escape mechanism technically unsatisfactory and scientifically incon- must also be postulated, because the menstrual cycle clusive. Subjects in different treatment groups are eventually reasserts itself even during full lactation. frequently ill-defined and few in number, with unsatis- The frequency of suckling may well prove to be a factory control groups or no control groups at all. key factor. A recent report (39) that high doses of Estimates of lactation performance are sometimes pyridoxine suppress the initiation of lactation even subjective or of dubious quantitative reliability. We more effectively than estrogens is of interest in this shall show below that the hypothesis that contra- context, in view of the known ability of that vitamin ceptive treatment has a measurable effect on lac- to assist the conversion of dopa to dopamine. It may tation is one that is extremely difficult, and perhaps thus have some influence on adrenergic tonus at the even impossible, to test in a scientifically definitive hypothalamic level, leading to increased production manner, and the foregoing critical comments on the of prolactin inhibitory factor. literature should be interpreted in that context. Other mechanisms to explain the influence of lac- Meanwhile, we have no option but to rely on the tation on fertility can, of course, be postulated-e.g., general impression conveyed by the literature as a effects on the endometrium or on cervical mucus. whole. We know of no investigations that have examined Most investigators have concluded that combined such possibilities. contraceptive pills or sequential preparations have an appreciable depressive effect on milk output, INFLUENCE OF CONTRACEPTIVE MEASURES whether measured in terms of the mother's own ON LACTATION impressions, or by test-weighing the baby, removal of milk by breast-pump, duration of lactation, or Present knowledge amount of supplementary food used. A minority Estrogens and their synthetic analogues, particular- say that there are no such effects, and there are a few ly , have been used by clinicians for many statements that milk flow is enhanced. Though it is years to suppress the onset of lactation in women often difficult to distinguish between alleged effects LACTATION 343 on the initiation of lactation and effects on the main- its unsatisfactory scientific nature, are: (a) that tenance of established lactation, these generalizations estrogens probably have some adverse effect on seem to apply to both phases. lactation-rather on the quantity and duration of Chopra (42)-summed up the situation as follows: milk flow than on its quality; (b) that any such "Current evidence suggests that certain types of effects are related to the estrogenic potency of the contraceptive pills do interfere with lactation, espe- compounds administered and are probably least cially those containing high doses of oestrogens and with modern combined pills of low estrogenic po- administered shortly after delivery (29, 53). They tency; (c) that adverse effects may not occur in all have a smaller inhibitory effect on established lac- women but may be clearly demonstrable only in a tation. At the lower ovulation-inhibiting doses cur- proportion of nursing mothers; (d) that, whereas it rently used in oral contraception, lactation may be is difficult on the present evidence to distinguish diminished but rarely stops altogether (54). Usually clearly between effects on the initiation and main- it is unaffected (55), particularly if the contraceptive tenance of lactation, estrogens given during the therapy is not started before the appearance of puerperal period are more likely to have adverse breast milk and breast-feeding continues (56) ",.a effects; (e) that there is so far no evidence that Some clarification of the current situation might progestins alone have any adverse effect on lactation, be achieved by classifying contraceptive pills in and some evidence that they have an enhancing influ- terms of relative potencies, as described by Heinen ence; and (f) that it is not yet possible to distinguish (57), rather than in terms of doses of specific oral from parenteral progestins in this respect. compounds. The majority view seems to be that it is the estro- Effect of hormonal contraceptives on the breast-fed gen component of the combined pills and sequential infant regimens that has an adverse effect on lactation. Curtis (66) described a case of gynaecomastia During recent years, oral or injectable progestins developing in a normal male infant whose mother have been under trial (45, 46, 58-63). In these reports, had started taking on the third day there is agreement that progestins alone do not post partum. Despite much publicity given to that impair lactation and that milk flow may even be report, no similar case has been published and many enhanced. of the authors cited above say that the infants devel- Evidence on milk composition is conflicting, but oped normally. This is to be expected, since recov- the general impression gained is that adverse effects, eries from the milk of mothers given radioactive sex if any, are trivial (49, 61, 64). have been of the order of 1 % or less (67-69). The intrauterine contraceptive device (IUD) has It has been known for several years that breast-fed also been implicated. Gomez-Rogers et al. (46) neonates may develop jaundice, apparently owing to asserted that, in Chilean patients fitted with such the presence in the milk of pregnandiol, which in- devices, lactation was significantly enhanced, with hibits conjugation of bilirubin in their (70, 71). 59 % still nursing 7 months after delivery, compared Wong & Wood (72) speculated that a possible cause with 43% among those in the control group. Sub- might be the use of hormonal contraceptives before sequently it was reported from India (65) that the pregnancy; this has been denied by Barnado et al. (73). average duration of lactation in women fitted with IUDs was 10.86 months, compared with 6.99 months Possibilities and limitations in further research for the control group; the average difference was, It will be clear from the foregoing that in our hoWever, not statistically significant. Gomez-Rogers opinion previous studies have been less than ade- et al. (46) suggested, on rather slender evidence, quate in scientific quality and that conclusions drawn that the mechanical stimulus of the IUD causes a from them must be highly tentative. We wish to neuroendocrine reflex leading to increased secretion make it equally clear that this is not intended as a of endogenous oxytocin, which in turn stimulates reflexion on the ability of the workers concerned milk flow. but as a recognition of the difficulties to be over- The general impressions we have gained from come. These may, indeed, be insoluble in practice. studying this literature, after making allowance for Human lactation and breast-feeding are notori- ously liable to influence by psychological as well a The reference numbers in this quotation have been as material factors. Ideally, therefore, a trial intended altered to correspond with those of the present article. to find out the nature and extent of a hypothetical 344 A. M. THOMSON ET AL. effect of a contraceptive agent should be of the fully controlled trial in women who had been ster- " double-blind" design and should be conducted in ilized immediately post partum and whose babies well-defined and adequately-sized groups of women, could receive adequate nutritional support in the forming "experimental " and comparable "con- event of lactational failure; but such groups would trol" groups, who are treated throughout the trial be difficult to assemble and would scarcely be in exactly the same way except for the treatment representative of the general population of lactating under examination. The nature of the treatment women. should not be made known to the experimenters or If fully controlled, scientifically definitive studies to the women until the trial has been concluded, of the effects of contraceptive measures on women in order to exclude any possibility of unintended during established lactation have to be ruled out, (perhaps unrecognized) psychological influences. we must continue to rely on comparative studies- It will be immediately obvious that a rigorous e.g., on the relative effects on lactation of one form trial conducted on such lines involves very serious of contraception compared with other forms, or the ethical difficulties. In our view, it is not ethical to effects of different doses of similar preparations. give placebo treatment to women who expect to be These might yield valuable information if the groups protected against unwanted pregnancies, or to give for study were carefully matched and of adequate contraceptive treatment to women who do not ask size, if the general management of mothers and for it. babies were uniform, and if great care were taken Double-blind, well-controlled trials are, however, to assess the adequacy of lactation by objective not completely ruled out on ethical grounds, and methods. One further point may be made. The inter- three have in fact been reported, all in women during pretation of past literature is greatly complicated by the first few days or weeks of gestation. Kaern (48), the wide variety of hormonal contraceptives used: in Denmark, using Norinyl 1 ( I mg, it is not uncommon to find that several different 0.05 mg) from the day after delivery to preparations have been used in one trial, in such the 8th post-partum day, with a partial follow-up a manner that possible different effects cannot be for 2 weeks after discharge from hospital, found a distinguished. It is to be hoped that, in future, significant difference in the proportions of women workers will concentrate their attention on a few who need to use complementary feeds on discharge. preparations, carefully chosen on the basis of contra- In USA, Miller & Hughes (51) followed women ceptive effectiveness with low estrogenic potency. for 5 weeks post partum. The experimental group Such preparations might be usefully compared with was given norethindrone 1 mg plus mestranol preparations containing progestins only, or with 0.08 mg from the 14th day, the control group other effective methods of contraception. Complete being given a placebo. Breast milk output (measured control, in the " double-blind " sense, might be by test-feeding) and mean weight gains of the babies unattainable, but it should at least be possible to were higher, and mean supplementary calories given obtain better information than we have at present. to babies were lower, in the placebo group than in the treated group, and the incidence of breast-feeding Practical trials at the end of 12 weeks was lowest in the treated As already indicated, some doubt remains as to group. In the Federal Republic of Germany, Semm the extent of the adverse effect, if any, of estrogen- (74) gave experimental subjects 2.5 mg containing contraceptives on lactation. Equal doubts plus mestranol 75 jig from the first post-partum day may be assumed to exist as to the extent of the and found no significant differences in milk pro- beneficial effects, if any, of progestins alone and duction or weight gains of babies, compared with of IUDs. But the evidence already available suggests subjects given a placebo pill. that adverse effects are likely to be rather small with It will be noted that these trials were made in low-estrogen combined pills, particularly if their use women in " developed " societies, where lactational is avoided during the period when lactation is not failure would pose no serious problems, and for short yet fully established. Our interpretation of the litera- post-partum periods when the risk of pregnancy ture has not persuaded us that estrogen-containing among control patients would be negligible. It would contraceptives should be avoided altogether in field not be ethical to conduct similar trials during the trials among populations where the maintenance of later stages of lactation or in less favoured social lactation for many months is nutritionally important. circumstances. One might, theoretically, conduct a Clearly, however, there is need for prudence. It LACTATION 345 might, for example, be deemed wise to avoid oral spacing between births-may lie in the realm of contraceptives with estrogen potencies above a pres- sexual behaviour. It is well established that in some cribed maximum; to use other forms of contra- communities there is a taboo-not always observed- ception (ifconsidered necessary on practical grounds) on intercourse during lactation, and there also may during the period when lactation is being estab- be more subtle alterations in sexual behaviour dur- lished; and to be vigilant for signs of inadequate ing lactation that help to determine fertility. lactation in individual mothers so that supplemen- Menstruation is the most accessible, though in- tary or alternative methods of feeding the baby can direct, index of the return of biological fertility dur- be instituted under supervision when necessary. ing lactation. As Fig. 2 shows, there are enormous Theoretical as well as practical considerations suggest differences between races and communities in the certain " critical " times. Thus, the risk of pregnancy, incidence of women reported to be menstruating at even without protection, is likely to be low during various stages of lactation. The nature-perhaps the first 6 weeks post partum; lactation is likely to even the reality-of such differences deserves examin- be well established towards the end of that time; ation. Is it possible that lactation " competes " with and it is common practice to conduct post-partum menstruation under marginal nutritional conditions? gynaecological examinations about that time. Again, If so, does this imply an effect on fertility? it can be expected that breast milk alone will become The real need is for more information on the progressively insufficient for the infant before it is return of ovulation after parturition, under varying 6 months old and, since measures for supplementary lactational conditions. Research on ovulation can feeding should have been instituted before that time, be undertaken only where the necessary cooperation the consequences of diminished milk flow can be from subjects can be maintained and where the neces- mitigated; on the other hand, the risks of further sary technical resources are available. The return of conception will have become so high, even during ovulation in fully, partly, and nonlactating women lactation, by 6 months post partum that effective should be investigated by measurements of basal family planning measures should already have been temperature and by endocrinological methods; the firmly established. frequency and strength of suckling should not be From a practical point of view, then, what seems overlooked as a possibly important variable. Funda- to be needed is field trials of methods likely to com- mental research on the hypothalamic control of bine the maximum protection for mothers and ovulation and its relationship to lactation is also babies with the fewest adverse side-effects. The cir- required. In view of the apparently reciprocal nature cumstances are likely to vary greatly in different of the control mechanisms, such research might places and at different times, so that no single pre- yield a new approach to contraception. scription is likely to be universally applicable. Contraception and lactation CONCLUSIONS It is difficult to organize adequately controlled and ethical field trials designed to elucidate possible Lactation and fertility antagonisms between hormonal contraceptives and The literature reviewed shows clearly that lactation the establishment of lactation. The best controlled per se provides an unreliable means of preventing (double-blind) studies have been limited to early conception and therefore cannot be considered as stages of lactation, so that it is not clear whether a satisfactory substitute for family planning by other the observed effects pertain to the maintenance as means. Prolonged lactation may nevertheless be well as to the establishment of lactation; and many associated with an important reduction of fertility of the other studies have been reported in such an rates in populations where family planning by reli- abbreviated fashion as to defy detailed analysis and able methods is exceptional. criticism. Whether the interval between parturition and the Despite such difficulties, there seems to be general return of biological fertility (fecundity) differs be- agreement that combined hormonal contraceptives, tween races is not clear; if there are ethnic differ- given cyclically or sequentially, have an adverse ences, they may be associated with differences in the effect on lactation, but one that with modern low- frequency of suckling permitted by the breast-feeding estrogen contraceptives is not usually obvious with- mother, or in the strength of sucking by the infant. out the careful collection of statistics. It is not A more powerful determinant offertility in practice- entirely clear whether this is a direct pharmacologi- 346 A. M. THOMSON ET AL. cal effect on the ability to secrete milk, or some form breast-feeding, could be used to secure valuable of unintended selection whereby mothers who use scientific information under different social circum- the pill are also those who fail to encourage frequent stances, as well as serving as " models " for refer- suckling, or who are psychologically less orientated ence in the future planning of services. towards sustained breast-feeding. Even less is it clear Family planning and maternal and child care are what dose-relationship exists between the hormones sometimes the business of separate branches of a given and lactation performance. Most workers medical service. They should be combined as far seem to agree that the estrogen component of com- as possible so that the same team that is responsible bined pills has an adverse effect on lactation and that for family planning is also responsible for supervis- progestins alone have no such effects. ing the mother while the infant is being fed from In our view, there is no need to consider that the breast or from the bottle. family planning by modem methods may have effects Possible physiological mechanisms to explain re- on lactation of such a degree as to be of serious lationships between lactation and fertility have been public health concern. Practical applications of discussed. There appears to be considerable scope contraceptive services, combined with support of for further research.

RJ:SUM12

LACTATION ET REPRODUCTION

I1 ressort nettement de la litterature que la lactation Le principal serait de recueillir plus de renseignements en soi ne constitue pas un moyen sfir d'empecher la sur la reprise de l'ovulation apres l'accouchement dans conception: on ne saurait donc la considerer comme diverses conditions de lactation. Les recherches sur l'ovu- pouvant se substituer d'une maniere satisfaisante aux lation ne peuvent etre entreprises que si la cooperation diverses methodes de planification familiale. Neanmoins, necessaire des sujets peut etre maintenue et si l'on dispose une lactation prolong&e peut etre associee a une reduc- des ressources techniques requises. II faudrait enqueter tion notable des taux de fecondite chez des populations sur la reprise de l'ovulation chez les femmes qui allaitent ou la planification familiale selon des methodes fiables totalement ou partiellement, ou qui n'allaitent pas, en est exceptionnelle. mesurant la temperature basale et en appliquant des On ne sait pas au juste si l'intervalle entre l'accouche- methodes endocrinologiques; la frequence et la force des ment et le retour de la f6condite biologique differe d'une tetees ne doivent pas etre n6gligees en tant que variables race a l'autre; s'il existe des differences ethniques, il se importantes eventuelles. Des recherches fondamentales peut qu'elles soient en rapport avec des differences sur le controle hypothalamique de l'ovulation et sur son concernant la frequence des tetees permises par la mere rapport avec la lactation sont egalement necessaires. allaitante ou la force de tetee chez le nourrisson. Peut-etre Eu egard au caractere apparemment reciproque des meca- est-ce dans le comportement sexuel qu'il faut rechercher nismes de controle, de telles recherches pourraient d6bou- un determinant plus actif de la fecondite dans la pratique, cher sur une nouvelle approche de la contraception. a savoir l'espacement des naissances. II est notoire que, II est difficile d'organiser sur le terrain des essais bien dans certaines collectivites, les relations sexuelles sont contr6les et conformes aux regles de la deontologie en interdites pendant la lactation - cet interdit n'etant vue d'elucider d'eventuels antagonismes entre les contra- toutefois pas toujours respecte - et il se peut qu'il y ait ceptifs hormonaux et une lactation bien etablie. Les aussi des modifications plus subtiles du comportement etudes les mieux contr6lees, faites selon la methode du sexuel pendant la lactation qui contribuent a determiner double insu, se limitaient aux premiers stades de la lac- la fecondite. tation, si bien qu'on ne sait pas au juste si les effets La menstruation est l'indice le plus accessible, quoique observ6s se rapportent a la poursuite de la lactation aussi indirect, du retour de la fecondit6 biologique pendant bien qu'a son etablissement; d'autre part, bien des etudes la lactation. On observe des differences consid6rables ont ete decrites d'une maniere tellement succincte qu'il d'une race et d'une collectivite a l'autre quant a l'inci- faut renoncer a les soumettre a une analyse critique dence des femmes qui ont leurs regles aux divers stades detaillee. de la lactation. La nature - voire la realit6 - de ces Nonobstant ces difficultes, il semble g6neralement admis difftrences merite d'etre examin&e. Est-ce possible que qu'une association de contraceptifs hormonaux, adminis- la lactation * concurrence) la menstruation dans des tres d'une maniere cyclique ou consecutive, exerce un conditions nutritionnelles marginales? Dans l'affirmative, effet adverse sur la lactation; toutefois, avec les contra- cela implique-t-il un effet sur la fecondite? ceptifs modernes a faible taux d'estrogene, cet effet n'est LACTATION 347 pas habituellement decelable en I'absence de statistiques de la sante publique. L'application pratique des services rigoureuses. I1 n'est pas absolument certain s'il s'agit contraceptifs, jointe a 1'encouragement de I'allaitement d'un effet pharmacologique direct sur l'aptitude a la au sein, pourrait etre mise a profit pour recueillir de secretion lactee ou de quelque selection non intentionnelle precieux renseignements scientifiques dans differents con- en vertu de laquelle les meres qui prennent la pilule sont textes sociaux, de meme que pour obtenir des ((modeles aussi celles qui n'encouragent pas le nourrisson a teter en vue de la planification des services dans I'avenir. frequemment ou qui, sur le plan psychologique, ont une I1 arrive que la planification familiale et la sante mater- moindre propension a l'allaitement prolonge. L'igno- nelle et infantile constituent des branches distinctes d'un rance est encore plus grande quant au rapport dose-effet service m6dical. Or, elles devraient etre combinees dans qui pourrait exister entre les hormones administrees et la mesure du possible afin que la meme equipe s'occupe les r6sultats de la lactation. La plupart des chercheurs a la fois de la planification familiale et de surveiller et semblent d'accord pour admettre que le constituant estro- de conseiller la mere pendant qu'elle nourrit son enfant gene des pilules mixtes exerce un effet adverse sur la au sein ou au biberon. lactation et que les progestines seules n'ont aucun effet On a cherche 'a determiner si des mecanismes phy- de ce genre. siologiques expliqueraient eventuellement certains rap- A notre avis, rien ne porte a croire que la planification ports entre la lactation et la fecondit6, mais il semble familiale selon les m6thodes modernes puisse influer sur que bien des recherches s'imposent encore dans ce do- la lactation d'une maniere inquietante du point de vue maine.

REFERENCES

1. SAUCIER, J. F. Correlates of the long post-partum 10. GIOIosA, R. Incidence of pregnancy during lactation taboo: a cross-cultural study. Current anthropology, in 500 cases. American journal of obstetrics and 13: 238-249 (1972). gynecology, 70: 162-174 (1955). 2. RAPHAEL, D. In: Correlates of the long post-partum 11. BAXI, P. G. A natural history of childbearing in the taboo: a cross-cultural study. Current anthropology, hospital class of women in Bombay. Journal of 13: 253-254 (1972). obstetrics and gynecology (New Delhi), 8: 26-51 3. DEL MuNDo, F. & ADIAO, A. C. Lactation and child (1957). spacing as observed among 2 102 rural Filipino 12. SANJUR, D. M. ET AL. Infant feeding and weaning mothers. Philippinesjournal ofpediatrics, 19: 128-132 practices in a rural pre-industrial setting. Actapaedia- (1970). trica Scandinavica, Suppl. 200 (1970). 4. BERMAN, M. L. ET AL. Effect of breast-feeding on 13. CANTRELLE, P. & LERIDON, H. Breast feeding, mor- post-partum menstruation, ovulation and pregnancy tality in childhood and fertility in a rural zone in in Alaskan eskimos. American journal of obstetrics Senegal. Population studies, 25: 505-533 (1971). and gynecology, 114: 524-534 (1972). 14. CHINNATAMBY, S. Effect of oral contraception on 5. MARTIN, W. J. ET AL. Intervals between births in a lactation. In: Hankinson, R. K. B. et al., ed. Nigerian village. Journal of tropical pediatrics and Proceedings of the 8th Intemational Conference on African child health, 10: 82-85 (1964). Planned Parenthood, Santiago, 1967. London, Inter- 6. BONTE, M. & VAN BALEN, H. Prolonged lactation national Planned Parenthood Federation, 1967, and family spacing in Rwanda. Journal of biosocial pp. 263-267. science, 1: 97-100 (1969). 15. DAS, S. K. & MITRA, A. K. A clinical-pathological 7. KAMAL, I. ET AL. Clinical, biochemical and experi- study of lactational amenorrhoea. Journal of obste- mental sudies in lactation. Lactation pattems in trics andgynecology (New Delhi), 16: 156-163 (1966). Egyptian women. American journal of obstetrics and 16. HYTrEN, F. E. & LEITCH, I. The physiology of gynecology, 105: 315-323 (1969). human pregnancy, 2nd ed. Oxford, Blackwell Scien- 8. DOUGLAS, J. W. B. The extent of breast feeding in tific Publications, 1971. Great Britain in 1946 with special reference to the 17. PETERS, H. ET AL. Lactation period in Indian women. health and survival of children. Journal ofobstetrics Fertility and sterility, 9: 134-144 (1958). and of the British Commonwealth, 57: 18. RAJALAKsHMI, R. Reproduction performance of poor 336-362 (1950). Indian women on a low plane of nutrition. Tropical 9. MCKEOWN, T. & GIBSON, J. R. A note on menstru- and geographical , 23: 117-125 (1971). ation and conception during lactation. Journal of 19. MALKANI, P. K. & MIRCHANDANI, J. J. Menstruation obstetrics and gynaecology of the British Common- during lactation. Journal ofobstetrics andgynecology wealth, 61: 824-826 (1954). (New Delhi), 11: 11-22 (1960). 348 A. M. THOMSON ET AL.

20. JAIN, A. K. ET AL. Demographic aspects of lactation 38. SELYE, H. & McKEoWN, T. Production of pseudo- and post-partum amenorrhea. Demography, 7: pregnancy by mechanical stimulation of the nipples. 225-271 (1970). Proceedings of the Society for Experimental Biology 21. SAXTON, G. A. & SERWADDA, D. M. Human birth and Medicine, 31: 638 (1934). interval in East Africa. Journal of reproduction and 39. FOUKAS, M. Laktationshemmende Wirkung des Pyri- fertility, Suppl. 6: 83-88 (1969). doxins [Lactation-inhibiting action of pyridoxine]. 22. POIrrER, R. G. ET AL. Applications of field studies Deutsche medizinische Wochenschrift, 97: 396-397 to research on the physiology of human reproduc- (1972). tion: lactation and its effects upon birth intervals in 40. STEELE, S. J. Inhibition of lactation by oestrogens. eleven Punjab villages, India. In: Sheps, M. C. & British medical journal, 4: 578 (1968). Ridley, J. C., ed. Public health and population 41. COWIE, A. T. The hormonal control of milk secretion. changes. Pittsburg, University of Pittsburg Press, In: Kon, S. K. & Cowie, A. T., ed. Milk: the 1965, pp. 377-399. mammary gland and its secretion, vol. 1. New York, 23. SALBER, E. J. ET AL. The duration of post-partum Academic Press, 1961, pp. 163-203. amenorrhea. American journal of epidemiology, 82: 42. CHOPRA, J. G. Effect of steroid contraceptives on 347-358 (1966). lactation. American journal of clinical nutrition, 25: 24. PEREZ, A. ET AL. Timing and sequence of resuming 1202-1214 (1972). ovulation and menstruation after childbirth. Popu- lation studies, 25: 491-503 (1971). 43. BHIRALEUS, P. ET AL. Effect of oral gestagens upon 25. SALBER, E. J. ET AL. Duration of post-partum amenor- lactation. In: Zatuchni, G. I., ed. Post-partum rhea in successive pregnancies. American journal of family planning: a report of the international pro- obstetrics and gynecology, 100: 24-29 (1968). gramme. New York, McGraw-Hill, 1970, pp. 345-356. 26. EL-MINAwI, M. F. & FODA, M. S. Post-partum lac- 44. BORGLIN, N. & SANDHOLM, L. Effect of oral contra- tation amenorrhea. American journal of obstetrics ceptives on lactation. Fertility and sterility, 22: 39-41 and gynecology, 111: 17-21 (1971). (1971). 27. ROBINSON, M. Failing lactation. A study in 1100 45. CASARES PONCE, H. J. Administraci6n continua de cases. Lancet, 1: 66-68 (1943). microdosis de clormadinona y sus effectos sobre la 28. LAMOTTE, G. Ovulation et post-partum chez la lactancia. Ginecologia y obstetricia de Mexico, 25: femme non lactante [Ovulation and the puerperium 295-299 (1969). in the non-breast-feeding woman]. Journal of gyne- 46. GOMEZ-ROGERS, C. ET AL. In: Hankinson, R. K. B. cology, obstetrics and biological reproduction, 1: 13-20 et al., ed. Proceedings of the 8th International Con- (1972). ference on Planned Parenthood, Santiago, 1967. 29. CRONIN, T. J. Influence of lactation upon ovulation. London, International Planned Parenthood Feder- Lancet, 2: 422424 (1968). ation, 1967, pp. 328-334. 30. TIMONEN, S. & LEHTO, L. The first menstrual period 47. IBRAHIM, A. & EL-TAWIL, N. Z. The effect of a new post partum. Annales chirurgiae et gynaecologiae low dosage on lactation. Fenniae, 52: 93-95 (1963). International surgery, 49: 561-565 (1968). 31. SHARMAN, A. Reproductive physiology of the post- 48. KAERN, T. Effect of an oral contraceptive immedi- partum period. Edinburgh, E. & S. Livingstone, 1966. ately post partum on initiation of lactation. British 32. UDESKY, I. C. Ovulation in lactating women. Ameri- medical journal, 3: 644-645 (1967). can journal ofobstetrics and gynecology, 59: 843-848 49. SUPORN, K. ET AL. The effects of injectable contra- (1950). ceptives on lactation. In: Clinical proceedings of 33. KEErrEL, W. C. & BRADBURY, J. T. Endocrine stud- First International Planned Parenthood Federation ies of lactation amenorrhea. American journal of South-East Asia and Oceanea Regional Medical and obstetrics and gynecology, 82: 995-1001 (1961). Scientific Congress, Sydney, 14-18 August 1972. 34. HUBER, VON A. & ULM, R. Probleme der Laktations- Melbourne, Australian and New Zealand journal amenorrhoea: Untersuchungen in Athiopien [Prob- of obstetrics and gynaecology. amenorrhea: studies in Ethiopia]. lems of lactation 50. KORA, S. J. Effect of oral contraceptives on lac- Gynaecologia, 153: 282-297 (1962). 20: 419-423 35. BROWN, J. B. Urinary excretion of oestrogens during tation. Fertility and sterility, (1969). pregnancy, lactation, and the re-establishment of 51. MILLER, G. H. & HUGHES, L. R. Lactation and menstruation. Lancet, 1: 704-707 (1956). genital involution effects of a new low-dose oral 36. KELLER, P. J. On the genesis of lactation amenor- contraceptive on breast-feeding mothers and their rhea. German medical monthly, 12: 546-547 (1967). infants. Obstetrics and gynecology, 35: 44-50 (1970). 37. COPPOLA, J. A. Brain catecholomines and gonado- 52. WALLACH, E. E. ET AL. Patient acceptance of oral tropin secretion. In: Martini, L. & Ganong, W. F., contraceptives: I. The American Indian. American ed. Frontiers in neuroendocrinology. New York, journal of obstetrics and gynecology, 97: 984-991 Oxford University Press, pp. 129-143, 1971. (1967). LACTATION 349

53. BONTE, M. Family planning by prolonged lactation tions. Journal of reproduction and fertility, 23: and hormones. Journal of tropical pediatrics and 513-515 (1970). African child health, 12: 56-58 (1966). 66. CURTIS, E. M. Oral contraceptive feminization in a 54. RICE-WRAY, E. ET AL. Oral progestins in fertility a normal male infant. Obstetrics and gynecology, 23: control. A comparative study. Fertility and sterility, 295-296 (1964). 14: 402409 (1963). 67. LAUMAS, K. R. ET AL. Radioactivity in the breast 55. GARCIA, C. R. & PINCUS, G. Clinical consideration milk of lactating women after oral administration of oral hormonal control of human fertility. Clinical of 3-H norethynodrel. American journal ofobstetrics obstetrics and gynecology, 7: 844-856 (1964). and gynecology, 98: 411-413 (1967). 56. KISTNER, R. W. Therapeutic application of proges- 68. VAN DER MOLEN, H. J. ET AL. Studies with 4-14C tational compounds. In: Marcus, S. L. & Marcus, lynestrenol in normal and lactating women. Acta C. C., ed. Advance of obstetrics and gynaecology, endocrinologica, 61: 255-274 (1969). vol. 1. Baltimore, Williams & Wilkins, 1967. 69. WIJMENGA, H. G. & VAN DER MOLEN, H. J. 4-14C 57. HEINEN, G. The discriminating use of combination mestranol in lactating women. Acta endocrinologica, and sequential preparations in the hormonal inhi- 61: 665-677 (1969). bition of ovulation. Contraception, 4: 393-400 (1971). 70. ARIAS, I. M. ET AL. Prolonged neonatal uncon- 58. KAMAL, I. ET AL. Clinical biochemical and experi- jugated hyperbilirubinemia associated with breast mental studies in lactation. II. Clinical effects ofgesta- feeding and a steroid, pregnane-3 (alpha), 20 (beta)- gens on lactation. American journal ofobstetrics and diol, in maternal milk that inhibits glucuronide for- gynecology, 105: 324-334 (1969). mation in vitro. Journal of clinical investigation, 43: 59. MARTINEZ-MANAUTOU, J. ET AL. Daily 2037-2047 (1964). for contraception: a clinical study. British medical 71. KRAUER-MAYER, B. ET AL. Ober den Frauenmilch- journal, 2: 730-732 (1967). induzierten Icterus prolongatus des Neugeborenen 60. ZAN4ARTU, J. ET AL. Fertility control with long acting [Prolonged icterus induced by the mother's milk in injectable steroids. Obstetrics and gynecology, 28: newborn infants]. Helvetica paediatrica acta, 23: 513-515 (1966). 68-76 (1968). 61. KARIM, M. ET AL. Injected progestagen and lac- 72. WONG, Y. K. & WOOD, B. S. B. Breast milk jaundice tation. British medicaljournal, 1: 200-203 (1971). and oral contraceptives. British medical journal, 4: 62. HEFNAWI, F. ET AL. Attempts to select a suitable 403-404 (1971). hormonal contraceptive during lactation. In: Pro- 73. BARNADO, D. ET AL. Breast milk jaundice and the ceedings of the Sixth World Congress of Obstetrics pill. British medical journal, 2: 348 (1972). and Gynaecology, New York, April, 1970. Baltimore, 74. SEMM, K. Contraception and lactation. In: Social Williams & Wilkins, 1970. and medical aspects of oral contraceptives. Amster- 63. KOETSAWANG, S. ET AL. Effects of oral contracep- dam, Excerpta Medica Foundation, 1966, pp. 98-101 tives on lactation. Fertility and sterility, 23: 24-28 (International congress series No. 130). (1972). 75. BAILO, P. & NOBILI, F. Allattemento e ovulazione. 64. TOAFF, R. ET AL. Effects of oestrogen and pro- Quaderni di clinica ostetrica e ginecologica, 20: gestagen on the composition of human milk. Journal 355-372 (1965). ofreproduction andfertility, 19: 475-482 (1969). 76. SHARMAN, A. Menstruation after childbirth. Journal 65. HINGORANI, V. & BAI, G. R. U. Lactation and lac- of obstetrics and gynaecology of the British Empire, tational amenorrhoea with post-partum IUCD inser- 58: 440-445 (1951).