Basal and LRH-stimulated secretion of FSH during early pregnancy.

The gonadotropin response to 25 mug of LH/FSH releasing hormone (LRH) intravenously was investigated during the very first weeks of pregnancy. It was found progressively to decrease, and no response in FSH was found for more than 5 weeks. The basal levels of FSH showed the same decreasing tendency, and a few weeks after conception they were often close to the sensitivity limit of the assay. With this report we have continued our description of the changing pituitary responsiveness to LRH from conception to the puerperium. During later stages of pregnancy the plasma levels of FSH were markedly reduced, and the response was inhibited even after 500 mug of LRH intervenously. The return of the response during the puerperium showed a specific pattern with a dissociation of the response in FSH and LH. No such dissociation was found during the period of progressive inhibition during the very first weeks of pregnancy.