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

Summary Introduction 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. Objectives This study aims to determine the incidence of antenatal hydronephrosis at our institution and the significance of third trimester scan in detecting CAKUT postnatally. Study design 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) ≥4 mm in the second trimester and ≥7 mm in the third trimester scan, diagnosed in the fetal medicine unit of our hospital, were included and were followed up postnatally for 6 months. Results 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 >10 mm, on the left side hydronephrosis, 87% had CAKUT on postnatal scan, and 85% with the right hydronephrosis had CAKUT. Conclusion Sixty percent cases of hydronephrosis detected in the second trimester scan resolve in utero . In the third trimester scan with RPD  10 mm, then the possibility of postnatal CAKUT is 86%. Table 1 . Incidence of hydronephrosis in 32 weeks scan as per the renal pelvic diameter Renal pelvic diameter (mm) Timing ( Timing (>32 weeks) Incidence of CAKUT in Postnatal scans Left Right Left Right Left Right 4–7 56 51 12 8 nil 1 (12.5%) 7–10 21 18 55 64 15 (27%) 16 (25%) >10 3 1 69 46 60 (87%) 39 (85%) Total 80 70 136 118 75 (55%) 56 (47%) Download high-res image (314KB) Download full-size image Flowchart 1- selection criteria (based on RPD) and number of cases recruited. RPD, renal pelvic diameter.