Flow velocity waveforms of the uterine artery in pregnancy: transvaginal versus transabdominal approach

Our objective was to compare recordings of flow velocity waveforms from the uterine artery via the transvaginal and transabdominal approach in normal human pregnancies. In a cross-sectional study from 16 to 40 weeks' gestation, 88 healthy pregnant women underwent a continuous-wave Doppler examination of their uterine arteries by both the transvaginal and the transabdominal approach. Measurements were recorded for both uterine arteries and averaged. Values recorded transabdominally were significantly lower than those obtained transvaginally in all patients < or = 27 weeks' gestation. From 28 weeks to term, transabdominal values remained lower, but the difference was smaller and insignificant, and noted only as a trend. Transvaginal velocimetry of the uterine artery produces significantly higher systolic:diastolic ratios than that of transabdominal recordings until 27 weeks' gestation. Thereafter, trophoblastic invasion of the uteroplacental circulation is maximal, and the difference between the values are minimal and insignificant. However, a pattern of lower resistance in the transabdominal approach remains consistent until term.