RELAXIN SECRETION IN IN-VITRO FERTILIZATION PREGNANCIES

OBJECTIVE: This study was designed to determine whether the late lutea l functional status of the corpora lutea in in vitro fertilization cyc les alters the secretion of relaxin during pregnancy. STUDY DESIGN: An alysis of serum relaxin, human chorionic gonadotropin, and steroid con centrations in sera of women with pregnancies viable beyond the twelft h week as a result of in vitro fertilization treatment was performed. RESULTS: The serum estradiol and progesterone concentrations decreased 5.5- and 4-fold from days 5 to 6 after human chorionic gonadotropin t o days 11 to 13 after human chorionic gonadotropin, respectively The s erum relaxin concentration increased 8-fold between the 11- to 15-day interval and the 16- to 50-day interval after human chorionic gonadotr opin and another 6-fold to the 51- to 90-day interval after human chor ionic gonadotropin (all p < 0.01). Multiple linear regression analysis showed that the serum estradiol level 11 to 13 days after human chori onic gonadotropin and the serum human chorionic gonadotropin level 11 to 15 days after human chorionic gonadotropin were the most powerful p aired predictors of the concentration of serum relaxin measured in the 11- to 15-day interval after human chorionic gonadotropin interval (R (2)=0.39, n=50), the 16- to 50-day interval (R(2)-0.61, n=51), and the 51- to SD-day interval (R(2)=0.55, n=39). CONCLUSION: Secretion of re laxin is determined by an interaction of the late luteal functional st atus of the corpora lutea and the human chorionic gonadotropin secrete d by the implanting pregnancy. These data allow for the hypothesis tha t inducing functional luteolysis by substituting one or more injection s of luteinizing hormone for the human chorionic gonadotropin injectio n may decrease secretion of steroids, relaxin, and other factors from the corpora lutea during pregnancy, decreasing the risk of premature d elivery in multiple gestations and the ovarian hyperstimulation syndro me.