Superior mesenteric artery blood flow velocimetry: Cross-sectional Doppler sonographic study in normal fetuses

Our objectives were to describe the flow velocity waveform of the fetal superior mesenteric artery and to establish a nomogram for its pulsatility index. In a cross-sectional study using color Doppler ultrasonography, superior mesenteric artery flow velocimetry was investigated prospectively in 96 healthy fetuses of between 14 and 37 weeks of gestation. In normal fetuses the pulsatility index measurements showed a slight but insignificant increase over the course of gestation (r = 0.26; P > 0.5). The lowest mean ± standard deviation for pulsatility index in the superior mesenteric artery was 1.86 ± 0.45 (95% confidence interval 1.67-2.06), recorded between 18 and 21 weeks' gestation. Thereafter the pulsatility index increased to 1.94 ± 6.4 (95% confidence interval 1.74-2.8) at 22 to 25 weeks, and from weeks 26 to 29 it increased to 2.18 ± 0.52 (95% confidence interval 1.91-2.46). During the third trimester and at term, the mean pulsatility index of 2.23 ± 0.32 (95% confidence interval 1.43-3.03) did not change significantly with gestational age. In normal fetuses, except for the early stages, a relatively stable vascular resistance of the intestinal circulation was found. The application of this nomogram in clinical practice may facilitate evaluation of intestinal perfusion in compromised fetuses with blood flow centralization.