The regulatory effect of estrogens on fetal growth: I. Placental and fetal body weights

Abstract

The influence of estrogen on placental and fetal growth was studied. White New Zealand pregnant rabbits were rendered estrogen deficient by a bilateral oophorectomy on the tenth day of gestation and given a daily dose of 5 mg. of progesterone intramuscularly up to the time of delivery. A second group similarly oophorectomized received the same dose of progesterone plus 2 μg estradiol-17β daily. A third group was sham operated and served as controls. Does from each of these groups were delivered at 21, 27, and 31 days of gestation. The total number of fetuses per litter as well as the number and weights of the live-born and their placentas were recorded in each instance. The results showed that in the estrogen-deficient pregnancies there was a significant increase in placental weight and in the placental to live-born weight ratio at all the periods of gestations studied. Live-born weight was also increased in the 27 and 31 day periods. An increase in stillbirth rate occurred in the estrogen-deficient group. It is concluded that estrogens regulate placental (and consequently fetal) size by exerting an inhibitory effect on placental growth. The mechanism by which this may be brought about is discussed.