Progesterone, 17-hydroxyprogesterone, estradiol, and estriol in late pregnancy and labor.

Levels of progesterone, 17 alpha-hydroxyprogesterone, estradiol, and estriol were measured in serial plasma samples collected from 30 uncomplicated pregnancies during the last eight weeks of gestation. From another group of 27 uncomplicated pregnancies, blood samples were collected during the second stage of labor and the same steroids were measured. Progesterone, 17-hydroxyprogesterone, and estradiol levels were highest during the last one to three weeks prior to the onset of labor, whereas estriol concentration increased progressively. The levels of these steroids during the second stage of labor were statistically not different from those just preceding labor. It is concluded that the onset of human labor is not associated with marked changes in the maternal levels of any of these steroids.