Relationships between prolactin and follicle-stimulating hormone during early pregnancy and the puerperium.

This investigation studies the relationship between the concentrationss of prolactin and FSH in the serum during pregnancy and the puerperium. A single dose of 5 mg bromocriptine during early pregnancy induced a profound fall in the serum level of prolactin with a substantial rise 20 h later. During the initial reduction in the concentration of prolactin, no alteration was noted in the level of FSH but during the subsequent increase in the prolactin concentration, there was a significant (P less than 0.05) decrease in the concentration of FSH. During week 1 of the puerperium, the concentrations of FSH and prolactin were significantly lower in lactating women than in women who were not breast feeding, but there was no significant difference between the concentration of FSH in women who had suppressed lactation with bromocriptine and in those whose lactation was suppressed by non-hormonal methods. when the concentration of FSH was measured every 10 min during a 30 min breast feed, there was a marked but short-lived rise in the serum concentration of prolactin but no change in the level of FSH. These results suggest that an increase in the serum level of prolactin in pregnancy can have a suppressive effect on the production of FSH. Although acute suckling-induced hyperprolactinaemia in the puerperium has no such effect, the maintenance of lactation in the long term does suppress the concentration of FSH in the serum.