Uterine Artery Doppler Reference Ranges in a Twin Caucasian Population Followed Longitudinally From 17 to 37 Weeks Gestation Compared to That of Singletons

Objectives: The primary aim was to measure uterine artery (UtA) indices in twin pregnancies of Polish Caucasian women and compare it with a previously published study by Geipel et al for DC twins (2011). The secondary aim was to find differences in UtA indices in MC, DC twins, and singletons.

Methods: A prospective longitudinal evaluation of UtA Doppler indices in 1462 examinations of twins and 5766 examinations of singletons between 17 and 37 gestational age (GA). Pulsatility index (PI) and resistance index (RI) were calculated.

Results: UtA PI and RI are lower in the twins than singletons but the analyzed mean values throughout gestation are higher than the study presented by Geipel et al. Obtained curves for DC twins and singletons had the same form as Geipel's curves. In MC twins, curves are flatter and characterized by lower differences throughout pregnancy than Geipel's curves for DC twins. They tend to be more similar about 32 weeks of gestations, resulting from different placenta structure in MC than DC twin pregnancies.

Conclusions: UtA Doppler indices in twin pregnancies are lower than in singletons. Obtained data have higher values for twins than reference charts proposed by Geipel's for dichorionic twins. We observed some differences between monochorionic and dichorionic twins' curves throughout pregnancy, but they were not significant.