Effects of fetal sex and weight and placental weight on maternal serum progesterone and chorionic gonadotropin concentrations.

A prospective study of 268 normal pregnant women at term was undertaken in which serum concentrations of progesterone (P) and chorionic gonadotropin (HCG) were determined zero to four days before spontaneous labor. Neither HCG nor P changed significantly during these four days, although they were not measured serially in most women. There was no correlation between the HCG level and either the placental or infant weight, infant sex, or maternal serum progesterone concentration. The maternal serum P level was slightly but significantly correlated with the weight of the placenta (r equal to 0.24; p smaller than 0.001) but not with the fetal weight or infant sex. Thus, although the mass of trophoblastic tissue contributed in part to P concentration, other intracellular factors such as the cyclic adenosine monophosphate system are probably more important regulating mechanisms.