Lack of release of human chorionic gonadotropin by thyrotropin-releasing hormone.

To assess the effect of TRH on the secretion of hCG, TRH in doses of 25 to 500 mug was administered to 10 pregnant women of 6 to 12 weeks or 16 to 20 weeks of gestation. There was no significant change in the serum hCG concentration during the ensuing 90 min. In women 6 to 12 weeks pregnant, doses of 25 mug, 100 mug, or 500 mug TRH elicted similar increments to serum TSH. Women 16 to 20 weeks pregnant had a slightly higher baseline TSH and a greater TSH response to TRH than the 6-12 week pregnant group. Although hCG may be an important thyroid stimulator in the first trimester of pregnancy, its secretion is not affected by TRH.