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When antenatal hydronephrosis (ANH, defined as antero-posterior pelvic diameter (APPD) ≥5-7mm) is diagnosed at the 20 weeks anomaly scan, (inter-)national guidelines recommend follow-up at 30 weeks. Fetuses with APPD ≥10mm are referred for postnatal work up. To evaluate the usefulness of these guidelines, we estimated the prognostic value of degree of ANH at the 20 and 30 weeks scan for postnatal urologic anomalies, surgery and solitary functioning kidney in our center.
We performed a historical cohort study of all fetuses with isolated ANH ≥5mm at the 20 weeks anomaly scan diagnosed between 2000 and 2009 at the Academic Medical Center. Cases were identified from the hospital owned prenatal database. Data of the 30 weeks follow-up scan were collected from the same database and findings of postnatal nephrologic examination of the infants from pediatric medical records. Logistic regression analyses were performed to study the association between degree of ANH at the 20 and 30 weeks scan and urologic anomalies after birth, need for surgical intervention, and disorders resulting in a solitary functioning kidney.
We identified 332 cases, of which 290 (87%) had complete data available for the 30 weeks scan and, when indicated, postnatal examination. In 192/290 cases (66%), APPD had normalized at the 30 weeks scan. Of the 98 cases with APPD ≥10mm at 30 weeks, 50/98 (51%) were diagnosed with urological abnormalities after birth. Of these 50 cases, surgical intervention was required in 26 (52%) and 12 (24%) ended up with a solitary functioning kidney. The odds of urologic anomalies, the need for surgery, and the occurrence of solitary functioning kidney all increased with the severity of ANH at the 20 as well as the 30 weeks scan (all p<0.001).
Screening for ANH at the 20 weeks scan allows early identification of neonates with urologic anomalies. Most cases of ANH at 20 weeks will have normalized at 30 weeks, thus the current criteria are on the safe side. However, the consequences of a urologic anomaly are such that guidelines should not be changed.