Mild renal pyelectasis in the second trimester: determination of cut-off levels for postnatal referral.

OBJECTIVE

To establish guidelines for postnatal referral of fetuses presenting with mild pyelectasis in the second trimester of pregnancy.

METHODS

In a retrospective study, 87 fetuses with a renal pelvis anteroposterior (RPAP) diameter of > or = 4 mm and < or = 10 mm before 28 weeks of gestation were included. All patients had a third-trimester scan and fetuses with an RPAP diameter of > or = 10 mm at that stage were referred for postnatal assessment. The family practitioner of all infants with an RPAP of < 10 mm in the third trimester was contacted for follow-up information. The RPAP diameter most predictive of renal pathology was determined with receiver-operating characteristics (ROC) curve analysis for both the first and second scans.

RESULTS

In 36 of 87 infants, 49 abnormal kidneys were diagnosed. Seven infants required surgery on eight renal tracts. The ROC curves of the first scan, second scan and differences between scans resulted in an area under the curve of 0.60, 0.87 and 0.85, respectively. The sensitivities and specificities for a cut-off level of 8, 9 and 10 mm at the second scan were 80%, 71% and 61% and 79%, 90% and 93%, respectively. At a cut-off level of 10 mm, only cases of insignificant minimal dilatation and a case of vesicoureteric reflux (VUR) requiring surgery were not detected.

CONCLUSION

After establishing a diagnosis of mild pyelectasis before 28 weeks, a second scan is mandatory to determine which infants need postnatal evaluation. A cut-off level of 8 mm has a low specificity but includes most cases of pathology. A cut-off level of 10 mm detects most significant pathology; however, VUR may not be detected.