Placental laterality and uterine blood flow at 20-40 weeks' gestation in low-risk pregnancies.

We sought to examine flow velocity waveforms of the uterine arteries with respect to placental location at 20-40 weeks' gestation. Blood flow (BF) volume, pulsatility index (PI), resistance index (RI), end-diastolic velocity, mean velocity, peak systolic velocity and systolic/diastolic ratio (S/D) were obtained by colour Doppler ultrasonography from bilateral uterine arteries in 288 low-risk singleton pregnancies. In cases with lateral placentation the mean PI and RI values at 36-40 weeks' gestation and the mean S/D value at 38-40 weeks were significantly higher in the contralateral than in the ipsilateral uterine arteries. Both BF volume and RI correlated inversely with gestational age in these groups (r = - 0.20 and p = 0.01; r = - 0.17 and p = 0.03, respectively). The contralateral and central uterine arteries were comparable for all Doppler indices. In conclusion, lateral placentation may affect uterine artery blood flow throughout gestation and some Doppler indices near term. Clinical significance of these findings needs to be elucidated.