Plasma prolactin concentrations during conception and the first ten weeks of human pregnancy

Plasma prolactin concentrations were measured daily throughout 20 cycles in which conception occurred and for several weeks during early pregnancy. Thirteen of the pregnancies were 'spontaneous' (i.e. without exogenous pharmacological stimulation) and 7 occurred during either clomiphene or bromocriptine treatment. Prolactin concentrations were fairly stable throughout the conception cycles until shortly after the time of the first missed menses. From this time concentrations rose gradually to reach a mean concentration of 1250 mU/l 60 days after ovulation. However, there were marked fluctuations from day to day within individuals and considerable variation in the magnitude of the prolactin rise between subjects. Three subjects were mildly hyperprolactinaemic and although prolactin levels remained slightly elevated throughout the study period, this did not affect the outcome of pregnancies.