The incidence of urinary tract dilation (UTD) is higher in preterm infants and is associated with adverse clinical outcomes. Understanding the risk factors for UTD can enhance management strategies in this vulnerable population. The objective of this study is to determine the association between clinical and laboratory variables and the occurrence of UTD in preterm infants.

This is a retrospective cohort study that analyzes data from 10,700 neonatal cases collected between September 2018 and June 2023. The study was conducted at the neonatal department of the Chinese PLA General Hospital. The final cohort consisted of 3,320 preterm infants. The study examined various exposures, including demographic factors, pregnancy and delivery details, maternal health conditions, medications, intrauterine events, and blood test indicators from preterm infants at birth. The main outcome was urinary tract dilation (UTD), defined by an anterior-posterior renal pelvic diameter (APRPD) ≥4 mm for infants born <28 weeks and ≥7 mm for those born between 28 to 37 weeks.

Out of 10,700 neonatal cases, 3,320 preterm infants were included after exclusions, with 179 (5.39%) diagnosed with UTD. Among them, 1,415 (42.62%) were female, with gestational ages between 23 and 37 weeks, and a median of 34 weeks (IQR: 32-35). Adjusted multivariate analysis showed that male preterm infants had a higher UTD risk than females (HR = 2.23, 95% CI: 1.58-3.13, P<0.001). Progesterone (HR = 3.13, 95% CI: 1.33-7.37, P=0.009), dexamethasone (HR = 1.52, 95% CI: 1.09-2.12, P=0.014), and ritodrine hydrochloride (HR = 2.59, 95% CI: 1.08-6.20, P=0.033) use during pregnancy increased UTD risk. Each unit increase in blood urea nitrogen to creatinine ratio (BCR) raised UTD risk by 3% (HR = 1.03, 95% CI: 1.01-1.05, P=0.007). Preterm infants with hemoglobin ≤120 g/L had a higher UTD risk than those with ≥146 g/L (HR = 2.34, 95% CI: 1.38-3.97, P=0.002).

The study found that male sex, maternal use of progesterone, dexamethasone, and ritodrine hydrochloride during pregnancy, as well as higher birth BCR and lower hemoglobin levels in preterm infants, are linked to a higher risk of UTD. This highlights the importance of careful maternal medication management and interpreting neonatal blood tests at birth.