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

Abstract

Our purpose was to determine the effects of fetal number, various ovulation induction treatments, and placental hormones on the concentration of maternal serum relaxin. The concentrations of relaxin, human chorionic gonadotropin, estriol, and alpha-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. 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 alpha-fetoprotein (all p < 0.01). 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 human chorionic gonadotropin. The serum relaxin concentration in twin pregnancies after treatment with follicle-stimulating hormone and luteinizing hormone (menotropins) (n = 10) was 3.3-fold that in twins resulting from spontaneous ovulation (n = 89, p < 0.01). In twins resulting from in vitro fertilization or gamete intrafallopian transfer (n = 9) the serum relaxin concentration was 2.6-fold higher than in twins resulting from spontaneous ovulation (p < 0.01). The effect of clomiphene citrate (1.2-fold, n = 7) failed to reach statistical significance. 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.