[A study on the maternal plasma C21 steroids concentration during pregnancy]

During pregnancy, C21 steroids such as progesterone (P4), and cortisol (F), have been reported to be closely involved in uterine contraction. To clarify the association between changes in steroid hormones and the onset of delivery, we measured the concentrations of six C21 steroids in maternal blood by high performance liquid chromatography. Changes in each steroid hormone were evaluated by analysis of variance during pregnancy. Pregnenolone, a source of C21 steroids, gradually increased during pregnancy. P4 and 17P4, its metabolite, reached a peak 3 weeks before delivery and noticeably decreased thereafter. Accompanying a decrease in P4 and 17P4, 20P4 and F, its metabolite, were noticeably increased. The association among these steroid hormones was also evaluated. The correlation between P4 and F was reversed after 3 weeks before delivery. These results suggest that steroid hormones in the maternal blood begin to change dynamically about 3 weeks before delivery. In particular, a decrease in P4 and an increase in F seem to be closely related to the onset of delivery.