Elevated plasma prolactin concentration in cholestasis of pregnancy.

The plasma concentrations of prolactin and estradiol-17 beta were measured by specific radioimmunoassays in 150 women with normal pregnancies and 76 women with cholestasis of pregnancy. At 33 to 34 weeks of gestation plasma prolactin concentrations were 187 +/- 23 ng/ml (mean +/- S.E.M.) for normal pregnancy and 341 +/- 38 ng/ml for cholestasis (p less than 0.001). At 35 to 36 weeks they were 254 +/- 24 and 355 +/- 26 ng/ml (p less than 0.01), and at 37 to 38 weeks 175 +/- 14 and 365 +/- 34 ng/ml (p less than 0.001), respectively. Higher prolactin levels in the cholestasis group were not related to differences in plasma estradiol-17 beta concentrations. No correlation was found between plasma prolactin and serum aminotransferase levels, or between prolactin levels and placental weight. The mechanisms by which plasma prolactin levels become elevated in cholestasis of pregnancy remain to be elucidated.