How Pregnancy Affects Blood Flow in the Kidneys: A Doppler Ultrasound Study

Abstract

Background: During pregnancy, the kidneys undergo significant physiologic and hemodynamic adaptations, such as increased renal blood flow and GFR. Renal Doppler ultrasonography is a non-invasive and reliable tool for monitoring these changes through measurements of some parameters like Resistive Index (RI) and Pulsatility Index (PI). But there are not enough regional data on trimester-specific changes of these indices especially in low and middle income countries, like Pakistan. Objective: This study was designed to investigate and compare parameters of Doppler ultrasound of renal arteries (RI and PI) in pregnant women in all trimesters, non-pregnant women, find local reference values and examine the changes in these parameters during pregnancy. Method: A cross sectional analytical study was done among 200 women (148 pregnant and 52 non-pregnant) at THQ Hospital Sabzazar, Lahore. Convenience sampling was used for the recruitment of participants. The Doppler measurement of the renal blood flow was performed using a Canon Xario 100 G ultrasound machine equipped with convex probe 3.5 MHz. Independent sample t-tests were used to compare pregnant and non-pregnant groups and one-way ANOVA was used to show differences between pregnancy trimesters. P value of < 0.05 was taken as significant. Results: The values of RI and PI were significantly lower in pregnant women than in non-pregnant women for both kidneys (p < .05). Right RI was higher in non-pregnant women (M = 0.63, SD = 0.05) compared to pregnant women (M = 0.59, SD = 0.05), t (198) = 3.10, p = .002, Cohen’s d = 0.60. Similar significant increases were observed for Right PI (p = .026), Left RI (p = .006), and Left PI (p < .001). In the trimesters, there were fluctuations but these were not statistically significant, so it did not show a consistent and progressive increase in vascular resistance with increasing gestation in this sample. Conclusion: The findings confirm that renal artery Doppler indices RI and PI significantly declined during pregnancy, with notable differences across trimesters. The changes are indicative of physiological adaptations and emphasize the need to have local reference values for correct interpretation.