Secretion patterns of plasma-progesterone, 17-hydroxyprogesterone and 20 alpha hydroxypregn-4-en-3-one in early normal pregnancy.

Plasma levels of progesterone, 17-hydroxyprogesterone and 20 alpha hydroxypregn-4-en-3-one were established from 4 to 16 weeks gestation by sampling 15 normal patients twice weekly. Apart from a peak at week 5, the mean levels of progesterone remained constant at about 24 ng/ml until week 10 and then rose progressively to 40 ng/ml at week 16.20 alpha hydroxypregn-4-en-3-one remained within the 7 to 9 ng/ml range apart from a peak at week 5. A significant decrease in mean levels of 17-hydroxy-progesterone was noted from week 5 to a nadir of 3 ng/ml at week 11. It would appear that the main hormone production of progesterones in pregnancy has been taken over by the placental unit by the 10th week.