Relationship between fetal urine production and amniotic fluid volume in normal pregnancy and pregnancy complicated by diabetes.

The hourly fetal urine production rate (HFUPR) was calculated from ultrasonic measurements of fetal bladder volume. A normal HFUPR reference curve, constructed from measurements in 189 normal pregnancies between 24 and 42 weeks gestation, showed a rapid increase of HFUPR from 3-3 to 24-4 ml up to 40 weeks followed by a slight decline. The amniotic fluid volume was estimated by the p-aminohippuric acid method within 12 hours of HFUPR measurements. In 67 normal pregnancies, there was no relationship between HFUPR and amniotic fluid volume measured between 36 and 41 weeks gestation. In 12 patients with fetal growth retardation, a relationship was found between reduced fetal urinary output and low amniotic fluid volume between 36 and 38 weeks gestation. In the 16 diabetic patients studied between 28 and 40 weeks gestation, there was no relationship between HFUPR (within or below normal range) and the high amniotic fluid volume (above 1500 ml in 13 patients). The implication of these findings are discussed.