Fetal pressure gradient estimations across the ductus venosus in early pregnancy using Doppler ultrasonography

Doppler ultrasonography was used to estimate the pressure gradient across the ductus venosus at 8-20 weeks of gestation. According to a cross-sectional study design, flow velocity waveform recordings were obtained from the umbilical vein and ductus venosus in 147 uncomplicated singleton pregnancies. Pressure gradients were calculated using the Bernoulli equation. The pressure gradient was estimated at 0.1-1.9 mmHg during ventricular systole and at 0-0.5 mmHg during atrial contraction. Time-averaged pressure gradients ranged between 0.1 and 1.3 mmHg. No statistically significant correlation could be established between the absence or presence of umbilical venous pulsations and estimated pressure gradient. Crude estimates of the pressure gradient across the ductus venosus can be established in the late first and early second trimester of pregnancy. The large scatter of data suggests limited accuracy of venous pressure gradient calculation in early gestation. However, it may also indicate that, in early gestation, venous hemodynamics function at very low pressures.