Ultrasonic assessment of fetal kidney function in normal and complicated pregnancies.

Fetal renal function was evaluated in 255 normal singleton pregnancies between 22 and 41 weeks of gestation and in 133 complicated pregnancies. Hourly fetal urinary production rate (HFUPR), fetal glomerular filtration rate (GFR), fetal tubular water reabsorption (TWR), and the effect of furosemide on fetal micturition was evaluated by ultrasound and a combination of ultrasound and biochemical tests. In normal pregnancies, the HFUPR increased from 2.2 ml/hr at 22 weeks of gestation to 26.3 ml/hr at 40 weeks of gestation. The fetal GFR was 2.66 ml/min at term, and the percentage of TWR was 78%. In complicated pregnancies, the HFUPR was above normal in 5.7% of the growth-retarded fetuses and below the tenth percentile in 58.6%. The GFR was below normal in 68.2% of the group of complicated pregnancies, but TWR did not significantly differ from that in the normal pregnancies. The effect of furosemide was the same in both growth-retarded and normal fetuses. In diabetic pregnancies, HFUPR values varied considerably and correlated with the fetal size. The HFUPR was normal in anencephalic fetuses and in 90.0% of the pregnancies with hydramnios.