Plasma prolactin levels during pregnancy.

Plasma prolactin levels in women who were between 8 and 40 weeks pregnant were determined by a homologous double antibody radioimmunoassay method. There were 980 samples from 839 uncomplicated and 213 samples from 116 complicated pregnancies. Prolactin levels in normal pregnancies varied from 6 ng/ml during early pregnancy to 210 ng/ml near term. A few values beyond the normal range were found in various groups of complicated pregnancies. About 14 per cent of samples from patients with threatened abortion and 7 per cent from patients with hypertension were above the upper normal range. The proportion of values below the 10th centile in patients with a low urinary oestrogen excretion was significantly higher than that in the normal population. Plasma prolactin levels did not seem to be a valuable guide to maternal or fetal well-being.