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Evaluation and follow-up of fetal hydronephrosis.

OBJECTIVE
To determine the antenatal course and neonatal follow-up of isolated fetal hydronephrosis.


METHODS
We reviewed our ultrasonography database from January 1989 to June 1999 for all cases of unilateral or bilateral fetal hydronephrosis that had at least 1 follow-up ultrasonographic examination. Cases were defined as mild, moderate, or severe depending on the renal pelvis anteroposterior diameter and gestational age. Data were analyzed using the chi2 test with the Fisher exact test where appropriate. Medical records were reviewed, and telephone interviews were performed to determine which infants received follow-up after birth.


RESULTS
Of 57,966 ultrasonographic examinations in 20,049 women during the study period, 393 patients met criteria for evaluation. Of these, 347 (88%) had fetuses with mild hydronephrosis. Most of these had complete resolution during the pregnancy. Forty patients had fetuses classified as having moderate hydronephrosis, and 6 patients had fetuses with severe hydronephrosis. Of those classified as moderate hydronephrosis, 15% resolved, 25% improved, 48% remained unchanged, and 12% worsened during the pregnancy. There were no cases of in utero resolution in the severe group; however, 4 of 6 cases improved to moderate or mild, and 2 cases remained unchanged. Of the cases identified prenatally, 25 received consultation by a pediatric urologist in the newborn period, and 7 of these required surgical intervention.


CONCLUSIONS
Our population-based data suggest that most cases of mild hydronephrosis will resolve before delivery. In contrast, cases of moderate or severe hydronephrosis are less likely to have resolution in utero and are more likely to worsen or remain unchanged. Of those fetuses with persistent hydronephrosis, only a small number required some surgical intervention after birth. This information is useful in counseling the patient whose fetus is noted to have isolated hydronephrosis.