Frequency of postnatal hydronephrosis in infants with a renal anterior–posterior pelvic diameter > 4 mm on midtrimester ultrasound

ObjectiveTo examine the association of antenatal renal pelvic dilatation observed on midtrimester ultrasound screening with the presence of hydronephrosis in newborn infants.Materials and methodsThe records of patients who received fetal ultrasound examination at 18–28 weeks' gestation from May 2008 to March 2012 were retrospectively reviewed. A fetal renal pelvic anterior–posterior (AP) diameter > 4 mm was considered abnormal and ≤ 4 mm was considered normal. On postnatal ultrasound, a renal pelvic AP diameter > 3 mm was considered to indicate hydronephrosis and ≤ 3 mm was considered normal. The association of postnatal hydronephrosis with prenatal pelvic AP diameter was determined using binary logistic regression analysis.ResultsThe study comprised 1310 newborn infants: 684 (52.2%) male and 626 (47.8%) female. Multivariate analysis showed a right or left prenatal AP renal pelvic diameter > 4 mm was associated with a higher risk of postnatal hydronephrosis compared with a right and left prenatal AP renal pelvic diameter ≤ 4 mm. Boys had a higher risk for postnatal hydronephrosis than girls (odds ratio = 2.42, p < 0.05).ConclusionAn antenatal renal pelvic AP diameter > 4 mm on midtrimester ultrasound is predictive of postnatal hydronephrosis.