Umbilical Artery Doppler Reference Indices in Normal Pregnancy

Background: Umbilical artery Doppler (UAD) studies offer a noninvasive method of indirectly assessing the fetal and uteroplacental circulation. However, the umbilical artery (UA) velocimetry reference currently in use was established in developed countries and derived from pregnant women that are likely to have had different biophysical characteristics. There is a need to develop an UA index nomogram for the indigenous pregnant population. Aim: The aim of this study was to determine the UAD reference indices among women with normal singleton pregnancy. Materials and Methods: This was a cross‑sectional descriptive study of 422 women with uncomplicated pregnancies who attended the antenatal clinic of the University of Abuja Teaching Hospital with pregnancy ages between 28 and 40 weeks’ gestation. The systolic and diastolic (S/D) ratio, the resistance index (RI), and the pulsatility index (PI) of the UA were obtained. Results: The mean UAD showed a progressive decrease with increasing fetal gestational age with S/D ratio, PI, and RI being 3.05 ± 0.28, 1.07 ± 0.1, and 0.68 ± 0.05 at 28 weeks and 2.10 ± 0.17, 0.73 ± 0.09, and 0.52 ± 0.04 at 40 weeks, respectively. Estimated reference values for relatively normal singleton fetuses S/D ratio, PI, and RI were 2.98, 1.03, and 0.67 and 2.07, 0.72, and 0.52 at 28 and 40 weeks of gestation, respectively. The S/D ratio (r = ‒0.741, P ≤ 0.002), PI (r = ‒0.694, P ≤ 0.001), and RI (r = ‒0.366, P ≤ 0.001) were significantly different from the existing reference value of 3.02 (S/D ratio), 1.05 (PI), and 0.62 (RI) and 2.18 (S/D ratio), 0.82 (PI), and 0.52 (RI). The respective existing values were at 28 weeks and 40 weeks of gestation. Conclusion: The UA index nomogram obtained from this study showed significantly lower values compared with the existing values, and therefore, it is advocated for use among African pregnant population.