Immunoreactive gonadotropin-releasing hormone level in maternal circulation throughout pregnancy.

Immunoreactive gonadotropin-releasing hormone was quantitated in maternal blood. Circulating levels of gonadotropin-releasing hormone were found to be significantly higher during pregnancy than in nonpregnant cycling women. The highest concentrations of gonadotropin-releasing hormone immunoreactivity were observed in the first half of pregnancy with values at 20 to 42 weeks being significantly lower. A correlation with placental human chorionic gonadotropin-releasing hormone concentrations and maternal circulating gonadotropin-releasing hormone levels was noted. Four pregnancies that resulted in premature labor and/or delivery had very low circulating maternal gonadotropin-releasing hormone concentrations, possibly reflecting placental dysfunction in these cases.