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t The (rnrn Ctrnt lIl Itle JANUARY 15. 1959 * VOL. 80 NO. 2 POLYHYDRAMNIOS AND separately. This is because there is much to suggest OLIGOHYDRAMNIOS* that the rates of formation and removal, as well as the origin and destination, of liquor amnii change T. N. A. JEFFCOATE,t M.D., F.R.C.S.E., with the progress of pregnancy. For example, the F.R.C.O.G. and J. S. SCOTT,t M.B., Ch.B., liquor is isotonic with plasma during the earlv M.R.C.O.G., Liverpool, Eng. months but becomes increasingly hypotonic in the later stages of pregnancy.24 Again, its urea, uric THEORIES CONCERNING the origin of liquor amnii acid and creatinine contents are similar to those were well reviewed by Shaw and Marriott36 in of plasma up to the fifth month; thereafter they are 1949 and do not require repetition. Suffice it to greater." say that most recent opinion has been coloured by For the present, the most important contribution observati;ons on the transfer of radioactive isotopes to knowledge made by radioactive isotope studies to and from the amniotic cavity, and especially by is the clear demonstration that the pool of liquor the studies reported by Vosburgh et al.41 These is not a static reservoir. Both the fluid and its workers concluded that the water content of chemical contents are in a state of continual flux, liquor amnii is completely exchanged every three passing to and from their surroundings. The volume hours. This conclusion, however, does n.ot tally of liquor, however, remains fairly constant for each wvith the clinical behaviour of women who sustain particular stage of pregnancy. The normal volume, a rupture of the membranes during pregnancy and and pathological variations constituting poly- who do not immediately go into labour. Such hydramnios and oligohydramnios, are likely to be women never lose fluid at the rate of one to two determined by the relative efficiency of the pints each three hours, as might be expected if mechanisms for production and disposal. liquor is formed so quickly. It is not always realized that Vosburgh's experi- ORIGIN OF LIQuoR AMNII ments on the rate of water exchange were limited to five women whose pregnancies varied in dura- From or Through the Membranes tion from 14 to 40 weeks. The results differed Liquor appears early in the pregnancy, when the videly from case to case, without any correlation fetal tissues are underdeveloped and non-func- according to the period of pregnancy, and the tional. Moreover, it is found within the sac of figure of 34.5% renewal of fluid per hour was blighted ova in which the fetus is absent or rudi- obtained by taking an average. The sodium ex- mentary. Such observations strongly suggest that change was studied in 20 pregnancies, the duration fluid enters via the membranes. Moreover, in early of which varied from 10 to 40 weeks; the findings pregnancy, liquor is so similar to plasma in com- were again reduced to an average to suggest a position that it could well represent a dialysate. complete turnover once in 14.5 hours, a rate of re- Amniotic epithelium is so constituted as to suggest newal five times less than that of the water. that it could have a secretory function; indeed, This work received a measure of confirmation by such a function has been demonstrated histo- Plentl and Hutchinson,'9 but the evidence from this logically.40 It is therefore possible that the amnion type of experiment is as yet so limited that the plays an active part in the formation of liquor. above figures should not be allowed to prejudice If liquor is regarded as a transudate in early preg- other observations. It would seem especially im- nancy and as the product of a selective secretory portant that all fututre investigations in this field, action of the amnion in the later months, the pro- whether they be by following the behaviour of gressive changes in its chemical and physical tracer substances or by physico-chemical analysis, properties might be explained. It is, however, dif- should be carried out for each phase of pregnancy ficult to conceive of the amnion producing or trans- mitting fluid in large amounts, because most of it *An elaboration of a, paper piresented by T. N. A. Jeffcoate is not in direct contact with a rich blood supply. to the Section of Obstetrics and Gynsecology of the Ontario Medical Association at Toronto, May 15, 1958. The exception is that portion of the membrane tFrom the Department of Obstetrics and Gynecology, Univer- sity of Liverpool. which covers the placenta, and it has been stig- 77 Canad. M. A. J. 78 JEFFCOATE AND SCOTr: POLYHYDRAMNIOS AND OLIGOHYDRAMNIOS Jan. 15, 1959, vol. 80 gested that this specialized area, with its extensive function is deficient-as it sometimes is during vascular connections, plays some part in liquor pregnancy and as it often is during labour. This production. The common association of poly- idea, reviewed by one of us (T.N.A.J.) in 1932, hydramnios with hemangiomatous tumours of the is supported by little more than conjecture. The chorion is quoted in support. This finding is capable newly born baby does not have to withstand' labour of different interpretations. Thus, McInroy and before voiding urine; it does so even when de- Kelsey23 concluded that, even in these cases, it is livered by elective Caesarean section. When the the fetus which is responsible for the hydramnios. fetal urethra is obstructed, the whole urinary tract They argued that the placental tumour occupies so becomes distended with quite large volumes of much of the intervillous space that it leads to fluid before labour, and that without there being placental insufficiency with retention of metabolites any evidence of placental failure. Nevertheless, within the fetus. These in turn stimulate the fetal even if the fetal kidneys normally secrete before kidneys to excrete abnormally large quantities of birth, it still remains possible that they pour out fluid into the amniotic cavity (see later). unusually large amounts of fluid when the func- tion of the placenta23 or of the maternal kidneys45 From the Fetus is grossly defective. The parts of the fetus which might secrete fluid Urine is reported to have been found in the into the amniotic cavity are the skin and its ap- fetal bladder as early as the 14th week of preg- pendages, the respiratory tree and the kidneys. nancy,24 and it is now generally accepted that the The main argument against a purely fetal origin kidneys are invariably capable of some function is that liquor is present early in pregnancy before by the 20th week. This timing may be of consider- most fetal organs are formed. This objection is able significance in explaining the reported pro- valid except in relation to fetal ectoderm which is gressive change in the chemical composition of present at a very early stage, which has the same liquor which commences about mid-pregnancy. origin as amnion, and which might conceivably Summation of the evidence suggests that, up to the have a similar function. Moreover, the volume of time the fetal organs are developed, liquor amnii liquor in early pregnancy varies directly with the is derived almost entirely from the amnion, or from surface area of the fetus.15 fetal skin and amnion. After mid-pregnancy, an additional and perhaps even more important Once fetal organs have developed, the production source of supply is the fetal kidneys, with possibly of liquor by the respiratory tract and kidneys, if a contribution from the fetal respiratory tract. It not by the skin, becomes feasible. The lungs are has to be recognized, however, that the composi- generally believed to be and in collapsed receipt tion of the excretion of the fetal kidneys differs of a relatively poor blood supply during the ante- from that of urine excreted after birth. The renal natal period. Alveolar secretion of fluid is there- filtration and concentration functions vary with fore presumably small, and a contribution from the the period of intrauterine development"' and also trachea and bronchi, although possible, is unlikely change progressively during infancy. Moreover, to be a major one. Nevertheless, Whitehead and certain components of the fetal renal excretion may others,"4 Macafee25 and Morison26 consider that, in be reabsorbed amnion. Such factors need at by the part least, the liquor amnii is derived from the to be considered when the results of chemical respiratory tract of the fetus. analysis of liquor amnii are interpreted. The fetal kidneys have attracted attention ever The importance of the renal contribution to the since Hippocrates postulated that liquor amnii is liquor during late pregnancy is further borne out fetal urine. That the kidneys can function before by study of cases of oligohydramniQs (see later). birth is made clear by the fact that a baby often voids urine immediately after birth, and by the finding of fluid in the bladders of approximately Tim DISPOSAL OF LIQUOR AMNII one-third of stillborn babies which come to Through the Membranes autopsy.20 Nevertheless, Holtermann'8 concluded The amnion might absorb as well as secrete that fetal urine does not contribute to the liquor fluid or, depending on osmotic pressures, at least amnii. He administered methylene blue to the allow a transudation back into the maternal circula- mother and recovered colourless liquor at delivery, tion. Whether production is a more important yet found the fetal urine stained with dye in the amniotic function than is disposal, and whether neonatal period. The test agent, however, was their relative importance varies with the stage of given only a short time before delivery and it now pregnancy, are unknown.

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