Fetal and maternal estrogen concentrations throughout pregnancy in the sheep

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Abstract
Because of the possible importance of estrogens in events of early pregnancy, and in fetal lung maturation and parturition, we have measured unconjugated estrone (E1) and estradiol (E2) concentrations in amniotic fluid (AF) and allantoic fluid (ALF) from pregnant sheep, and have compared these values with estrogen concentrations in the fetal and maternal plasma. Samples were collected under acute conditions of general anaesthesia or from chronically catheterized animals during late pregnancy. E1 always exceeded E2 in AF and ALF. On days 100 to term, the concentrations of E1 sulphate in AF and ALF greatly exceeded those of E1 but decreased towards term. E1 was elevated in AF on day 50, decreased to day 100, and in chronic preparations increased significantly before birth, at the time of the prepartum rise in E1 in maternal and fetal plasma. E1 in ALF was higher than in AF on days 50 and 100, but no consistent pattern of E1 in ALF with gestation was established, due in part to substantial interanimal variation. Similar concentrations of E2 were found in AF and ALF. In AF, E2 rose significantly before birth, with a similar time course to the prepartum rise in E2 in maternal and fetal plasma. In early pregnancy, the ratio E1/E2 in umbilical cord blood was higher than in all other compartments. We conclude (1) there is evidence for estrogen production in early pregnancy (day 50), favouring E1; (2) E1 predominates over E2 in the fetal as well as maternal compartment, although its concentration in amniotic and allantoic fluid is substantially less than E1S; (3) parturition is preceeded by rising concentrations of E1 and E2 in AF as well as in maternal and fetal plasma; and (4) this increase probably reflects rising fetoplacental production and may indicate increasing estrogen availability to the fetal membranes, uterine and fetal tissues around the time of birth.

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