Relationship between fetal weight and placenta

The relation of fetal and placental weight under different conditions was studied by Westermark on a material of 20,000 cases, using mathematical formulas, and he came to the following conclusions: fetal weight is less at first birth than at subsequent birth and is independent of the age of the mother; the placenta of full-term fetuses weighs on average 644.0 in boys and 657.0 in girls; the ratio of placental to fetal weight in boys is 1: 5.47, in girls 1:5.17; fetal weight arrives faster than placenta weight; the number determining the proportion between fetal weight and placenta weight increases with maternal age, but is independent of the number of former pregnancies; it is greater in twins.