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Placental Insufficiency J Postgrad Med J: first published as 10.1136/pgmj.38.438.225 on 1 April 1962. Downloaded from POSTGRAD. MED. J. (1962), 38, 225 PLACENTAL INSUFFICIENCY J. C. MCCLURE BROWNE, B.Sc., M.B., B.S., F.R.C.S.Ed., F.R.C.O.G. Professor of Obstetrics and Gynecology, University of London; Director, Department of Obstetrics and Gynaecology, Hammersmith Hospital, London, W.iz THE term placental insufficiency has been in- The situation of the placenta within the uterus creasingly used in recent years in Britain to is first determined by outlining the area of the describe a condition where the foetus is particularly uterus which shows greatest radio-activity after an at risk, or dies, antepartum, intrapartum or some- intravenous injection of 10 microcuries of radio- times postpartum, without trauma. Postmortem sodium 24Na. If the placenta or part of it is found examination of the child shows that it is entirely to be situated on the anterior wall of the uterus, it healthy and the only changes demonstrable are is then possible to investigate further. After the those of anoxia, namely multiple petechial haemor- lapse of a few days to allow elimination of all radio- rhages, and the presence of meconium and liquor activity due to the placental localization, 5 micro- in the lungs. The placenta may show distur- curies of 24Na are injected into the intervillous bance, for example infarction or abruptio, or it space, and the time taken for the injected sodium may be unduly small. On the other hand it may to be carried away by the circulation is recorded. seem perfectly normal. Such silent intra-uterine In a normal healthy woman at 38 weeks half of the death is common in pre-eclamptic toxamia or in injected sodium is removed in about 20 seconds. by copyright. hypertension, and it is occasionally seen when the If hypertension or toxemia is present the rate of only abnormality is that the pregnancy is pro- clearance is substantially reduced, so that half of longed beyond the normal span. the injected dose may require as much as 60 seconds for its removal. This shows very clearly Placental Ischaemia that in the presence of hypertension or of pre- On the basis of animal experiments Page eclamptic toxaemia there is a measurable degree of (1939), Bastiaanse and Mastboom (I949) and placental ischaemia. Morris, Osborn and Wright Beker (I949) all suggested that placental ischaemia (1955), using a modification of our technique, was the causative factor. Evidence of the oc- showed that a similar reduction in blood flow http://pmj.bmj.com/ currence of placental ischaemia in the human has occurred in the uterine muscle in toxamia, and we however only comparatively recently been pre- ourselves showed that the same occurred in the sented. Greenfield, Shephard and Whelan (I951) presence ofhypertension without toxsemia. Cox and calculated that to supply the oxygen requirements Chalmers (1953) and Johnson and Clayton ()955) of a foetus weighing 3,000 g., 350 ml. of maternal have also shown that in these conditions transfer of blood must flow through the placental bed each sodium across the placenta to the foetus is con- minute. Villee (I954) reached almost the same siderably slowed, and Clemetson and Churchman conclusion. Assali, Douglas, Baird, Nicholson (1954) found that the transfer of amino-acids was on September 25, 2021 by guest. Protected and Suyemoto (I953) inserted a catheter in a similarly impaired. On the other side of the uterine vein in the human and found, using placenta Walker and Turnbull (I953) showed that nitrous oxide and the Fick principle, that at 38 in these conditions the foetus is short of oxygen. weeks the amount of maternal blood flowing It is clear therefore that in toxaemia and hyper- through the uterus was 750 ml. per minute. tension there is placental impairment which may Metcalfe, Romney, Ramsey and Reid (I953), amount to insufficiency. by a similar method found a slightly lower figure. In our own series, although the amount of Our own work (Browne and Veall, 1953) showed maternal blood (normally 600 ml. per minute), that under normal conditions at 38 weeks 600 was reduced in cases of toxamia or hypertension to ml. of maternal blood were supplied to the as little as 200 ml. per minute, no babies were lost. placenta each minute, so that it seemed that the It is apparent therefore that under normal condi- major portion of blood entering the uterus went conditions the placenta has a very considerable to the placenta. Details of our technique have functional reserve, and moreover that the foetus been published elsewhere, but it may be of in- has various means of counteracting the adverse terest to recall it in general terms. effects of placental insufficiency. Only when the Postgrad Med J: first published as 10.1136/pgmj.38.438.225 on 1 April 1962. Downloaded from 226 POSTGRADUATE MEDICAL JOURNAL April I962 placental function is very seriously impaired, and evident why these two conditions when combined the foetus has used to the full all its powers of carry a considerable risk for the foetus. will fcetal death occur. compensation, Other Factors Diminished Placental Permeability Several other factors impair the efficiency of the Impairment of the maternal circulation to the placenta: placenta is one cause of placental insufficiency. I. Age. There is good evidence that the blood Another cause is diminished placental permea- pressure rises steadily with age. Thus in a survey bility. Flexner, Cowie, Hellman, Wilde and of the blood pressure of 7,000 primigravidae Vosburgh (1948) showed that the rate of transfer (Browne I961) the mean blood pressure at the age of sodium from mother to foetus is impaired in late of 20 was 124/73, rising steadily to 130/76 at the pregnancy, and the nearer to term the greater the age of 40. It is also well known clinically that the degree of impairment. This seems to be a normal older woman runs a greater risk of losing her baby ageing process in every placenta, and is aggravated from no obvious cause. It seems reasonable, if the pregnancy goes beyond term. when we remember the effect of hypertension on the maternal placental circulation, to suppose that Liquor Volume the less resilient circulation of the older woman should give rise to placental insufficiency. Recent work by Elliott and Inman (I96I) in my 2. Gravidity. There seems to be no doubt that own Department has shown that the volume of the the primigravida and grand multipara are more liquor amnii reflects the functional capacity of the likely to have a silent intrauterine foetal death than placenta. Thus they found that in a healthy women having their second or third children. It woman the volume of the liquor reached a peak may be that in the primigravida the circulatory (1,o00 ml.) at 37 weeks, diminishing steadily there- to the demands of after until at 42 weeks there was only about 300 ml. responses pregnancy are not clinician fully met as pregnancy is a new experience for her. altogether. Every knows from his own The grand multipara on the other hand, thoughby copyright. experience that in some cases of prolonged preg- knowing what is demanded of her, is unable be- nancy when the membranes rupture there is vir- cause of a degenerating vascular system to tually no liquor, and what little there is is thick and to these respond stained with meconium. In tox- fully demands. pre-eclamptic 3. Exercise. The beneficial effects of rest in the aemia and in hypertension Elliott and Inman found management of toxaemia and of hypertension in that the volume of liquor at 37 weeks was less than pregnancy have been known for generations. Morris in the normal woman (approximately 800 ml.) and and others (1956) showed that exercise resulted in the reduction in volume proceeded more rapidly considerable than so that volumes of to 200 slowing ofthe uterine circulation. He normal, 0oo ml. first determined the rate of clearance of 24Na fromhttp://pmj.bmj.com/ were found between 40 and 41 weeks. Elliott's the uterine muscle of women at rest, then during findings suggest that the volume of the liquor exercise, and finally at rest again. In every case amnii reflects accurately the functional state of the the slowing of uterine circulation produced by placenta, and volumes below 300 ml. suggest that exercise was very marked, and moreover the return the fcetus is in grave danger from placental in- to normal on cessation of exercise was slow. It sufficiency. will readily be seen that the effect of physical on a uterine and activity placental circulation on September 25, 2021 by guest. Protected Twin Pregnancy already impaired by hypertension or prolonged Though I have not yet been able to prove it I pregnancy may be lethal for the foetus. strongly suspect that placental insufficiency occurs 4. Labour. Wright, Morris, Osborn and Hart particularly in twin pregnancy, and that in this case (1958) also showed very clearly that during labour it is of dual origin, for Morris, Osborn, Wright and the uterine circulation was impaired and that the Hart (1956) found that uterine blood flow was some- degree of impairment increased the longer the what slower in twin pregnancy, and undoubtedly labour went on. Caldeyro Barcia (1959), using they combined weights of the foetuses being greater our own method, showed that during a uterine than that ofa single foetus there is a greater demand contraction the maternal placental blood flow was for oxygen to cross the placenta. I consider there- diminished. This may well account for many of fore that in twin pregnancy the optimum duration is the cases of foetal distress and even fcetal death 38 weeks and not 40 weeks.
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