Functional capacity of the gonadotrophs during pregnancy and the puerperium

The nature of secretion of gonadotropin during pregnancy and the puerperium was determined by measuring plasma levels of beta-subunit luteinizing hormone (GnRH) during the first, second, third trimesters of pregnancy, and at 10 days post partum in lactating and nonlactating women. The nonlactating subjects were divided into two groups according to whether hormonal suppression of lactation was used. Baseline and response levels of beta-LH and FSH after GnRH were below the limits of assay sensitivity (less than 0.5 ng/ml and less than 1.5 mlU/ml, respectively) in all pregnant subjects. In contrast, postpartum lactating and nonlactating subjects who received no hormonal treatment for suppression of lactation had a small but significant increase in FSH after GnRH. In lactating women, FSH increased from 1.5 +/- 0.3 mlU/ml to 2.7 +/- 0.3 mlU/ml (p less than 0.05); and in nonlactating subjects, FSH increased from undetectable levels to 2.0 +/- 0.4 mlU/ml (p less than 0.001). Patients who received estrogenic compounds for suppression of lactation had undetectable FSH baselines and no response after GnRH. beta-LH in both lactating and nonlactating women had a variable but not a significant response to one administration of GnRH. In conclusion, our findings indicate that the functional capacity of the gonadotrophs recovered earlier (at 10 days) than previously reported (less than 14 days) after term pregnancy, and the recovery of FSH secretion occurs earlier and is more consistent than the recovery of beta-LH.