Objectives: The purpose of this study was to evaluate the importance of renal abnormalities first identified in the third trimester of pregnancy after normal findings on a detailed second-trimester structural fetal survey.
Methods: Between March 1, 2007, and August 1, 2009, all patients having a sonographic examination in the third trimester who previously had normal findings on a second-trimester detailed structural fetal survey were retrospectively identified. Fetal renal abnormalities first detected in the third trimester and not seen during the second-trimester survey were tabulated. Neonatal follow-up was obtained for those with sonographic abnormalities.
Results: Overall, 4170 patients had third-trimester scans after normal findings on a detailed second-trimester survey. A new renal abnormality was detected in 77 (1.8%) of these third-trimester scans. Detailed postnatal imaging follow-up was available in 49 of 77 (63.6%), of which 44 (89.8%) had prenatal hydronephosis. Of these, 9 of 44 (20.5%) had reflux; 14 of 44 (31.8%) had normal findings or had hydronephosis that resolved on follow-up sonography after birth; and the rest had hydronephosis (13 of 44 [29.5%]), ureterovesical junction obstruction (3 of 44 [6.8%]), or ureteropelvic junction obstruction (5 of 44 [11.4%]). The other 5 fetuses with nonhydronephrotic renal abnormalities had pelvic kidneys (3) and unilateral renal agenesis (2). Two of those with reflux (22.2%) required surgery, and 1 of those with ureterovesical junction obstruction (33.3%) required surgery.
Conclusions: Most renal abnormalities first identified in the third trimester after normal findings on a detailed second-trimester structural fetal survey were hydronephrosis, of which approximately one-third resolved after birth. Among the remaining neonates with persistent hydronephrosis, almost one-third had reflux that was not detected on the second-trimester anatomy scan.