Can early ultrasonography explain the lower miscarriage rates in twin as compared to singleton pregnancies following assisted reproduction?

Objective: To compare first trimester 2D conventional and 3D power Doppler angiography measures in twins and singletons following assisted reproduction. Methods: We prospectively evaluated 50 singleton and 47 twin pregnancies that eventually ended in live births. Patients were recruited from a single assisted reproductive technology (ART) center with standard treatment protocols. Obstetric ultrasound was performed at 8-9 weeks + 6 days. Intervillous flow, uteroplacental circulation and uterine artery pulsatility (PI) and resistance index (RI) using two-dimensional (2D) ultrasound examination were evaluated. Using three-dimensional (3D) power Doppler angiography, placental volume and the 3D power Doppler indices from the intervillous and uteroplacental circulation were calculated. Results: Demographic and cycle characteristics were similar in mothers of singletons and twins. - Placental volume was significantly (1.6-fold) larger in twins. Vascular density and blood perfusion in the intervillous space were lower in twins. The comparison of the other parameters did not show significant differences between singletons and twins. Conclusion: The data confirm the larger placental volume in twins, denoting a probable higher production of placental hormones that would support an early twin pregnancy. The lower vascular density and blood perfusion in the intervillous space in twins may also confer a reproductive advantage to them.