Estrogen metabolism in normal and pregnant women.

The pattern of estrogen metabolism in human pregnancy differs materially from that of the nonpregnant woman in that estrogen production is very great and the output of estriol is disproportionately increased with respect to the other metabolites (1). To obtain information about this latter alteration, the fate of estradiol has been studied in both pregnant and nonpregnant women. It was found that to all purposes the exogenous hormone was metabolized indistinguishably by the two groups of women. Estimates of the daily endogenous production of estradiol*,’ i.e. “the secretion rate” (4) were obtained in five pregnant subjects from the specific activity of the urinary metabolites, estrone, estradiol, and estriol, and compared with the results obtained in a normal young woman after the administration of a very small amount of estradiol-17b labeled with tritium. In the normal young woman the daily secretion rate was similar when calculated from any one of these three metabolites. In the pregnant subjects, although the secretion rates calculated from estrone and estradiol were in good agreement, that calculated from estriol was very considerably greater. The implications of these findings are discussed.