THE ROLE OF RELAXIN IN THE DEVELOPMENT OF THE UTEROPLACENTAL CIRCULATION IN EARLY-PREGNANCY

Objective: To evaluate the relation between the development of the ute roplacental circulation as assessed by Doppler velocimetry and the mat ernal blood relaxin concentration. Methods: Transvaginal color Doppler investigation of the uteroplacental circulation was performed in 42 h ealthy women at 6-15 weeks' gestation before termination of pregnancy for psychosocial reasons. The resistance index (RI), pulsatility index (PI) and maximum peak velocity were recorded at the level of the main uterine artery, and the presence of intervillous now was noted. Relax in, hCG, 17 beta-estradiol (E2), and progesterone levels were measured in maternal venous blood. Results: Limited intervillous flow was note d from 10 weeks' gestation and continuous intervillous now from 12 wee ks. An inverse relation was observed between the circulating levels of both E2 and progesterone and uterine artery RI and PI, whereas the re laxin level correlated positively with uterine RI and PI. Estradiol an d progesterone levels also correlated positively with uterine peak sys tolic velocity and intervillous blood now. Multiple linear regression analysis indicated that both hormones contributed to the decrease in d ownstream resistance to uterine blood now with advancing gestational a ge, as assessed by uterine RI. In addition, relaxin contributed to the uterine RI and PI and to the intervillous blood now. Conclusion: Thes e data suggest that relaxin, E2, and progesterone may influence the ch anges in uterine blood now that occur in early pregnancy. The role pla yed by E2 and progesterone in the development of the uteroplacental ci rculation may be modulated by relaxin, constituting a novel function f or this ovarian peptide.