The effect of ovulation induction on the concentration of maternal serum relaxin in twin pregnancies

Abstract OBJECTIVE: Our purpose was to determine the effects of fetal number, various ovulation induction treatments, and placental hormones on the concentration of maternal serum relaxin. STUDY DESIGN: The concentrations of relaxin, human chorionic gonadotropin, estriol, and α-fetoprotein were determined in blood samples drawn at 16 to 18 weeks for prenatal diagnosis in 72 singleton and 115 twin pregnancies and analyzed by one-way analysis of variance, correlation analysis, and stepwise multiple linear regression of the log-transformed data. RESULTS: The maternal serum concentrations of each of the four measured hormones were significantly higher in the twin pregnancies than in the singleton pregnancies: 1.4-fold for relaxin, 1.9-fold for human chorionic gonadotropin, 1.9-fold for estriol, and 2.2-fold for α-fetoprotein (all p p n = 10) was 3.3-fold that in twins resulting from spontaneous ovulation ( n = 89, p n = 9) the serum relaxin concentration was 2.6-fold higher than in twins resulting from spontaneous ovulation ( p n = 7) failed to reach statistical significance. CONCLUSIONS: The second fetus causes a 1.4-fold increase in the concentration of maternal serum relaxin in twin pregnancies. Induction of ovulation with menotropins causes an additional 3.3-fold increase, whereas in vitro fertilization or gamete intrafallopian transfer treatment causes an additional 2.6-fold increase over that seen in twin pregnancies that followed spontaneous ovulation. (AM J OBSTET GYNECOL 1996;174:227-32.)