Uterine Artery Doppler Resistance before and during Pregnancy: Insights from an African Population

OBJECTIVE: This study assessed the extent of uterine artery resistivity during pregnancy compared to the nonpregnant state and established reference ranges for an African population. METHODS: A multicenter observational study was conducted, involving 745 females (pregnant and nonpregnant) in Ghana. Transabdominal Doppler ultrasound assessments were performed to measure resistive index (RI) and pulsatility index (PI) in the nongravid and pregnant women presenting for prenatal ultrasound at different gestational stages. Statistical analyses, including Kruskal-Wallis tests and multiple linear regression, were used to evaluate differences in Doppler indices. RESULTS: The mean PI and RI for the nongravid uterus are 2.07 and 0.77, respectively. In the first trimester (<12 weeks), PI declines by 31.93%, while RI decreases modestly by 9.28%. By 12-16 weeks, PI and RI decline further by 44.25% and 12.81%, respectively, suggesting ongoing arterial remodeling. The most significant drop occurs between 17-24 weeks, where PI falls by 64.54% and RI by 22.22%, reflecting substantial vascular dilation. After 24 weeks, the PI declines beyond 70% decline and the RI beyond 24%. CONCLUSION: These findings establish critical reference benchmarks, where deviations from expected declines may indicate a pregnancy complication warranting closer clinical monitoring.