Significance of third trimester ultrasound in detecting congenital abnormalities of kidney and urinary tract—a prospective study

Abstract

Antenatal hydronephrosis is defined as dilatation of the renal pelvis with or without dilatation of calyces in the developing fetus. Although second trimester scan is more sensitive in detecting congenital abnormalities of kidney and urinary tract (CAKUT), it has been suggested that the third trimester scan is more predictive of postnatal outcome. This study aims to determine the incidence of antenatal hydronephrosis at our institution and the significance of third trimester scan in detecting CAKUT postnatally. It is a prospective observational study. During the 3-year study period from June 2013 to May 2016, all cases of antenatal hydronephrosis, defined as renal pelvic diameter (RPD) ≥4mm in the second trimester and ≥7mm in the third trimester scan, diagnosed in the fetal medicine unit of our hospital, were included and were followed up postnatally for 6 months. In the fetal medicine unit, 32,443 women were screened for anomalies, and hydronephrosis was detected in 269 cases. Incidence of antenatal hydronephrosis was observed to be 0.83% in our institution. In second trimester scan, of 80 cases with the left hydronephrosis, only 22 (27.5%) had postnatal CAKUT and of 70 cases with the right hydronephrosis, 18 (25.7%) had CAKUT. In the third trimester scan, it was observed that with RPD >10mm, on the left side hydronephrosis, 87% had CAKUT on postnatal scan, and 85% with the right hydronephrosis had CAKUT. Sixty percent cases of hydronephrosis detected in the second trimester scan resolve in utero. In the third trimester scan with RPD <10mm, the possibility of postnatal CAKUT is 23%, whereas if RPD is>10mm, then the possibility of postnatal CAKUT is 86%.