Variations in plasma steroid and prostaglandin concentrations during human pregnancy.

Radioimmunoassay of sex steroids and prostaglandins was performed on plasma obtained from 10 uncomplicated primigravid subjects at a stated time of the day at varying stages of gestation. Prostaglandin E2 (PGE2), prostaglandin F2alpha (PGF2alpha), oestrone and oestriol concentrations reached a peak a few weeks before term and then declined. Progesterine, 17-hydroxyprogesterone and oestradiol increased during pregnancy particularly after 32 weeks. In two normal patients repeated blood samples were taken throughout the day at weekly intervals in late pregnancy for sex steroid assays to evaluate the variation of concentrations with the time of sampling and the significance of changes in mean concentrations of different steroids with approaching parturition. Marked variability was found in the levels of different steroids during the day. Plasma oestriol values were lowest at 8.00 a.m. in one patient sampled frequently. A marked decrease in oestriol, oestrone, oestradiol and 17-hydroxyprogesterone was found in one patient prior to the onset of spontaneous labour. In another subject there was no decrease in concentrations of oestrogens or progestogens prior to induction of labour at term.