1 Department of Obstetrics and Gynecology, Afzalipour Hospital, Afzalipour Faculty of Medicine, Kerman University of Medical Sciences, Kerman, Iran

2 Department of Fetomaternal, Faculty of Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran

3 Medicine Specialist in Preventive and Social Medicine, Head of family health in department of health. Tehran University of Medical Sciences, Tehran, Iran

flow with hourly urine output and amniotic fluid volume in fetuses with a gestational age of 30 to

34 weeks in normal pregnancies.

Methods: This cross-sectional study was conducted on 95 eligible pregnant women who were

referred for their routine third-trimester care from March 2022 to March 2023. In each fetus,

resistance (RI) and plausibility (PI) indexes of the umbilical and renal artery, the amniotic fluid

volume, kidney size, and hourly urine output were recorded. The hourly urine production was

calculated by considering bladder volume differences at a 30-minute duration.

Results: With gestational age increasing, amniotic fluid volume (p-value=0.005), and the hourly

urine output (p-value=0.005), were increasing significantly. RI of umbilical (p-value=0.022),

right (p-value<0.001) and left (p-value=0.001) renal arteries and PI of right (p-value=0.042) and

left (p-value=0.001) renal arteries decreased significantly through the pregnancy. There was a

negative linear association between RI and PI of the renal arteries with hourly urine output. The

results showed that mean of renal artery Doppler indices including right and left RI (0.87 ± 0.08

vs. 0.88 ± 0.07, p-value=0.274) and right and left PI (2.52 ± 0.59 vs. 2.56 ± 0.64, p-value=0.614)

was the similar in both sides. In adjusted linear regression analysis, two variables of gestational

age and renal artery RI were significantly (p-value<0.001) associated with hourly urine output.

Conclusion: It seems the fetus's renal artery Doppler findings and urine outputs represent fetal renal

function, warning the physicians about post-natal evaluation after birth.