Progesterone concentrations in maternal and fetal blood.

Progesterone concentrations in cord artery and vein and in retroplacental and maternal blood were measured in 43 women delivered by caesarean section. The cord vein concentration was consistently higher than the cord artery concentration. The two were correlated but neither was related to the concentration in retroplacental blood. It was concluded that progesterone is secreted by the placenta independently to the mother and the fetus. No role for fetal progesterone was evident from the data.