Maternal plasma and amniotic fluid levels of estradiol, estrone, progesterone, and prolactin in early pregnancy.

During the 16th to 20th weeks of gestation, maternal plasma (mean) level of estradiol is 5.2 ng/mL; estrone, 3.0 ng/mL; estriol, 2.1 ng/mL; progesterone, 4235 ng/dL; and prolactin, 74 ng/mL. Amniotic fluid levels are: estradiol, 446.8 pg/mL; estrone, 234.1 pg/mL; progesterone, 5200 ng/dL; and prolactin, 2633.5 ng/mL. Maternal prolactin concentrations correlate with plasma estradiol. Amniotic fluid prolactin levels correlate significantly with maternal plasma concentrations of estradiol and estrone. The mechanisms for the possible relationship between maternal estradiol and pituitary and decidual tissue production of prolactin are discussed.