Hemodynamics of the umbilical artery and conceptus-related measurements in singleton and twin pregnancies in ewes.

In sheep, adequate physiological maternal adaptations to twin fetuses are key for their prenatal development. We hypothesized that there is a relationship between maternal circulating steroid hormone concentration, hematocrit, and patterns of conceptus growth and umbilical artery hemodynamics in twin vs singleton pregnancies. Ewes carrying singletons (n = 6) or twins (n = 7) were selected. Hematocrit, progesterone (P4 ) and estradiol-17β (E2 ) concentrations were analyzed. Blood flow of the umbilical artery (UBF) was assessed through Doppler ultrasonography. Ewes carrying twins had a decreased (p = 0.03) hematocrit. There was a tendency (p = 0.08) for ewes carrying twins to have increased P4 from day 20 to 40. From day 50 to 70, P4 tended to be increased (p = 0.07) and E2 was increased (p = 0.01) in ewes carrying twins. From day 90 to 120, ewes carrying twins had greater (p ≤ 0.04) P4 . Ewes carrying twins had increased (p < 0.01) P4 and tended to have (p = 0.06) increased E2 . From day 60 until 110, placentomes from twins were larger (p ≤ 0.05). On day 50, UBF was greater (p = 0.04; 27.38 vs. 20.95 ± 1.99 ml/min) in twins. It has been suggested that physiological adaptations during early pregnancy can significantly impact fetal development in multiple offspring carrying ewes. Our findings suggest that increased umbilical artery blood flow early in gestation, associated with increased maternal concentrations of P4 and E2 , and decreased hematocrit (related to plasma volume) could contribute to those adaptations.