ESTROGEN AND PROGESTIN METABOLISM IN PREGNANCY. I. SPONTANEOUS AND INDUCED LABOR1

Abstract

Analyses of urine specimens from 22 normally pregnant women during the last 10 wks. of pregnancy reveal that at some time between 8 and 24 days prior to labor a max. efficiency in the production and conversion of estrogen and progestin is reached. Between this peak period and the onset of labor a progressive change in steroid metabolism occurs, characterized by progestin and estrogen withdrawal and attributable to a gradually decreasing rate of production and conversion and some increase in the rate of destruction of these placental steroids. The onset of true labor coincides with a sudden decrease in conversion and increase in destruction of estrogens. Findings on 1 patient who experienced false labor reveal that, although uterine contractions may be. initiated without any evidence for a sudden increase in estrogen destruction, a relative hormonal deficiency at the period which is normally one of max. production and conversion may increase the sensitivity of the uterine musculature. Uterine contractions themselves result in a rapid reduction in the rate of estrogen and progestin production and conversion and a striking increase in their rate of destruction. This same change in steroid metabolism was apparent during a 5-hr. period of labor artificially induced by rupture of the membranes. Possible causes for the pre-partum withdrawal of estrogen and progestin and the physiol. significance of the changes in steroid metabolism which precede and accompany labor are discussed.