THE INFLUENCE OF PLACENTAL SIZE ON FOETAL GROWTH IN MAN, WITH SPECIAL REFERENCE TO MULTIPLE PREGNANCY

Abstract 1. The association between placental and foetal weights in man is examined in 4931 single and 834 twin maternities. 2. After 30 to 31 weeks' gestation, both foetuses and placentae are heavier in single than in twin pregnancy (see Table 1). 3. At the same placental weights singletons are heavier than twins. The difference in foetal weights is reduced, but not eliminated, by standardization of the means to correct for differences in distribution by duration of gestation (Fig. 2). 4. It is concluded that in man something more than the difference in placental weight is required to explain the difference between growth rates of twins and singletons in late pregnancy. Data published by Ibsen [1928] are used to show that in the guinea-pig also, retardation of foetal growth in large litters cannot wholly be attributed to variation in placental size (Fig. 4). 5. Mean weekly increment in weight of singletons between birth and 3 months (0·49 lb.) is almost identical with that of single foetuses between 30 and 36 weeks gestation (0·48 lb.), when foetal growth is linear. This suggests that the retardation of growth of the single foetus (from about 37 weeks) is determined, as in multiple pregnancy, by the inability of the pre-natal environment fully to meet the needs of the foetus, rather than by the inability of the foetus to maintain its rate of growth.