THE EFFECT OF OVULATION INDUCTION ON THE CONCENTRATION OF MATERNAL SERUM RELAXIN IN TWIN PREGNANCIES

OBJECTIVE: Our purpose was to determine the effects of fetal number, v arious ovulation induction treatments, and placental hormones on the c oncentration of maternal serum relaxin. STUDY DESIGN: The concentratio ns of relaxin, human chorionic gonadotropin, estriol, and a-fetoprotei n were determined in blood samples drawn at 16 to 18 weeks for prenata l diagnosis in 72 singleton and 115 twin pregnancies and analyzed by o ne-way analysis of variance, correlation analysis, and stepwise multip le linear regression of the log-transformed data. RESULTS: The materna l serum concentrations of each of the four measured hormones were sign ificantly higher in the twin pregnancies than in the singleton pregnan cies: 1.4-fold for relaxin, 1.9-fold for human chorionic gonadotropin, 1.9-fold for estriol, and 2.2-fold for alpha-fetoprotein (all p < 0.0 1). The concentrations of each of the four hormones were significantly correlated with each of the others and with the number of fetuses (p < 0.01), except that estriol was not significantly correlated with hum an chorionic gonadotropin. The serum relaxin concentration in twin pre gnancies after treatment with follicle-stimulating hormone and luteini zing hormone (menotropins) (n = 10) was 3.3-fold that in twins resulti ng from spontaneous ovulation (n = 89, p < 0.01). In twins resulting f rom in vitro fertilization or gamete intrafallopian transfer (n = 9) t he serum relaxin concentration was 2.6-fold higher than in twins resul ting from spontaneous ovulation (p < 0.01). The effect of clomiphene c itrate (1.2-fold, n = 7) failed to reach statistical significance. CON CLUSIONS: The second fetus causes a 1.4-fold increase in the concentra tion of maternal serum relaxin in twin pregnancies. Induction of ovula tion with menotropins causes an additional 3.3-fold increase, whereas in vitro fertilization or gamete intrafallopian transfer treatment cau ses an additional 2.6-fold increase over that seen in twin pregnancies that followed spontaneous ovulation.