Corpus Luteum Function in Early Pregnancy

The plasma levels of progesterone, 17-hydroxyprogesterone (17-OHP) and HCG were measured serially after the induction of ovulation by gonadotropins with resulting single pregnancies. The plasma steroid levels increased until peak concentrations were attained at 3–4 weeks of gestation; then both steroids declined at the same rate. The plasma progesterone level reached a nadir at 6–8 weeks, after which it increased again as a result of placental secretion. By contrast, plasma 17-OHP levels continued to decline until a level somewhat higher than normal luteal phase values was reached. Plasma HCG was increasing throughout the period that plasma progesterone and 17-OHP were declining. The data suggest that the corpus luteum of pregnancy functions maximally during the first 4 weeks following ovulation, and that its functional life span may be about 10 weeks. The lack of correlation between plasma HCG levels and steroid secretion raises important questions about the control of function of the corpus luteum of early pregnancy.