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胎儿的发育是和进行气体交换、摄取营养的胎盘表面面积的大小有密切关系。包括人类在内的若干哺乳动物,一般胎儿大小和胎盘大小之间成正相关,胎儿小胎盘也小,相反,胎儿大胎盘也大。由动物试验得知,如果胎儿和胎盘的大小不成正相关时胎儿容易发生异常。例如有报告将孕猪一侧子宫和卵巢切除,则胎盘重量减少,胎仔体重/胎盘重量值就增加,与此同时胎仔死亡率也增加。人类也同样,胎盘小了,其重量在平均值减2个标准差以下
The development of the fetus is closely related to the size of the placenta surface area for gas exchange and nutrition intake. Several mammals, including humans, have a positive correlation between the size of the fetus and the size of the placenta. Small fetuses have small placentas. On the contrary, large placentas are also large. Animal experiments show that if the size of the fetus and placenta are not positively related to the fetus prone to abnormalities. For example, there are reports of uterine and ovariectomized pigs on one side, then reduce the weight of the placenta, fetal weight / placental weight value increases, while fetal death rate also increased. Similarly, in humans, the placenta is small and its weight is reduced by less than two standard deviations from the mean