Mild pyelectasis: evaluating the relationship between gestational age and renal pelvic anterior-posterior diameter

To determine the relationship between gestational age and renal pelvic anterior-posterior diameter and the feasibility of developing gestational age-specific thresholds for the diagnosis of mild pyelectasis.

Cross-sectional study of 420 singleton fetuses between 16 and 39 weeks' gestation. The mean renal AP diameter as a function of gestational age was determined using fractional polynomial regression models and centile plots were generated. Assessment of goodness of fit for each regression model was performed.

There was a positive correlation between gestational age and renal pelvic AP diameter (Pearson's Correlation Coefficient 0.65). Using the derived mean and standard deviations of renal AP diameter, gestational-age specific 95% reference levels were generated. The sensitivity, specificity, positive, and negative predictive values of using the gestational age-specific cutoffs for predicting persistent postnatal renal anomaly were 80%; 99%; 29%; and 99% respectively.

There is a positive correlation between gestational age and renal pelvic AP diameters. Reliable gestational age-specific renal AP thresholds for diagnosis of pyelectasis are provided.