Objective: To test the hypothesis that superovulation results in elevated maternal circulating relaxin concentrations throughout the second and third trimesters of pregnancy, independent of the pattern of hCG secretion.
Methods: Two groups of women with singleton gestations were studied: a group of nine women who achieved pregnancy after stimulation with human menopausal gonadotropin and a group of six women who achieved pregnancy without prior stimulation. Peripheral blood samples were drawn approximately every 5 weeks throughout the second and third trimesters. Serum relaxin concentrations were measured using a human relaxin-specific enzyme-linked immunosorbent assay; hCG was measured by an immunofluorometric assay.
Results: The stimulated group had significantly higher relaxin levels throughout pregnancy (P=.007, multivariate analysis of variance) than did nonstimulated controls. The mean relaxin level in stimulated patients was 1.78 ng/mL (95% confidence interval [CI] 1.5, 2.17) and in nonstimulated subjects the level was 0.73 ng/mL (95% CI 0.59, 1.25). Spline fits demonstrated that stimulated patients had higher relaxin levels throughout the second and third trimesters. There was no significant difference in hCG concentrations between the two groups (P=.61).
Conclusion: In singleton gestations after superovulation, maternal serum relaxin concentrations are significantly higher throughout the second and third trimesters of pregnancy. These differences are independent of the pattern of hCG secretion. It appears that luteal relaxin secretion is controlled by factors in addition to hCG.