ELEVATED MATERNAL SERUM RELAXIN CONCENTRATIONS THROUGHOUT PREGNANCY IN SINGLETON GESTATIONS AFTER SUPEROVULATION

Objective: To test the hypothesis that superovulation results in eleva ted maternal circulating relaxin concentrations throughout the second and third trimesters of pregnancy, independent of the pattern of hCG s ecretion. Methods: Two groups of women with singleton gestations were studied: a group of nine women who achieved pregnancy after stimulatio n with human menopausal gonadotropin and a group of six women who achi eved pregnancy without prior stimulation. Peripheral blood samples wer e drawn approximately every 5 weeks throughout the second and third tr imesters. Serum relaxin concentrations were measured using a human rel axin-specific enzyme-linked immunosorbent assay; hCG was measured by a n immunofluorometric assay. Results: The stimulated group had signific antly higher relaxin levels throughout pregnancy (P =.007, multivariat e analysis of variance) than did nonstimulated controls. The mean rela xin level in stimulated patients was 1.78 ng/mL (95% confidence interv al [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 pati ents had higher relaxin levels throughout the second and third trimest ers. There was no significant difference in hCG concentrations between the two groups (P = .61). Conclusion: In singleton gestations after s uperovulation, 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 appea rs that luteal relaxin secretion is controlled by factors in addition to hCG. (C) 1998 by The American College of Obstetricians and Gynecolo gists.