Cystic lesions of the fetal kidney: diagnosis and prediction of postnatal function by fetal urine biochemistry.

Fetal urine was aspirated under ultrasound control from 21 large cystic renal masses in 18 pregnancies of 20 to 35 weeks gestation. None were associated with bladder or ureteric dilatation. At postnatal investigation, 12 kidneys were demonstrated to be hydronephrotic (5 with no or poor function) and 9 multicystic. Urinary concentrations of sodium (Na+), calcium (Ca++), and phosphate (PO4--) were significantly higher in the multicystic group than in the hydronephrotic, whereas urea and creatinine levels were lower. Determination of urinary PO4-- enabled differential diagnosis with no false-positive or false-negative cases. Among hydronephrotic kidneys, no biochemical parameter accurately predicted postnatal function, although creatinine was increased in all three nonfunctioning kidneys. In hydronephrotic kidneys, urinary Na+ concentration increased with advancing gestational age (r = .66; P < .02), suggesting that the duration of hydronephrosis has a negative effect on renal function.