Ureteropelvic junction obstruction in utero and ex utero.

Seventy cases of ureteropelvic junction obstruction, bilateral or unilateral, were followed prospectively throughout gestation and postnatally for an average of 2.3 years. Cases of ureteropelvic junction obstruction with a renal pelvis dilated less than 1 cm uniformly did well; those with a pyelectasis more than 2 cm, both bilateral and unilateral, had a favorable outcome in approximately three-quarters. Surprisingly, pelvis dilatation between 1-2 cm had a better outcome if bilateral than if unilateral.