A combined ultrasonic and biochemical study of fetal renal function in the term fetus

Fluid and electrolyte balance in extremely preterm infants <24 weeks of gestation in the first week of life

BACKGROUND

Extremely preterm infants, especially those <24 weeks of gestation, displayed extremes in changes of fluid/electrolyte balance. The purpose of the present study was to retrospectively investigate abnormalities in fluid/electrolyte balance during the first postnatal week.

METHODS

Of 32 subjects admitted during 20 years, 17 infants with no severe complications were examined, and 72 appropriate-for-dates infants at 24-28 weeks of gestation were taken as controls. The subjects were managed in closed incubators in a highly humidified environment and fluid/electrolyte balances were monitored in retrospect.

RESULTS

The subjects had higher urine contents, while the insensible water loss was higher than in controls. As for weight loss, no remarkable changes were noted between the two groups. On day 4 and thereafter, serum Na(+) levels were high, indicating a high complication rate of hypernatremia without differences in hyperkalemia. The decrease in blood base excess was rapid, requiring supplementation of sodium bicarbonate up to postnatal day 5 in all preterm infants.

CONCLUSION

Due to the relatively higher urine output and insensible water loss in extremely preterm infants during postnatal week 1, higher water intake was required. As such, metabolic acidosis was bound to have occurred.

Measurement of fetal urine production in normal pregnancy by real-time ultrasonography

Serial measurements of fetal bladder volume were obtained by real-time ultrasonography at 2- to 5-minute intervals, and the hourly fetal urine production rate was calculated. The mean hourly fetal urine production rate increased from 5 ml/hr at 20 weeks' gestation to 51 ml/hr at 40 weeks. These values are double those reported in previous studies that measured fetal bladder volumes at 15- to 30-minute intervals because the cycle length is shorter than previously thought.

Fetal kidney volume and urine production in cases of fetal growth retardation

The amount of amniotic fluid has a close correlation to the function of the fetal renal system. In many cases of fetal growth retardation oligohydramnios is obvious. The aim of this study is the investigation of the hourly fetal urine production rate (HFUPR) and the growth of fetal kidneys during pregnancy in cases of fetal growth retardation and to evaluate the renal participation in the origin of oligohydramnios in cases of growth retardation. In 52 healthy pregnancies and 27 cases with known fetal growth retardation, the volume of the fetal kidneys was measured sonographically and the hourly rate of fetal urine production was determined. Two third of the patients with fetal growth retardation had obvious oligohydramnios. In cases of fetal growth retardation the volume of the fetal kidneys was significantly smaller when compared to the control group, and the volume of fetal urine production was significantly lower. The reduced perfusion of the fetal kidneys in those cases with fetal growth retardation may be the reason for the reduction of the HFUPR. Due to the fact that HFUPR is a dynamical parameter and in close relationship to the perfusion of the fetal kidneys, the identification and measurement of this parameter may help to detect subacute and imminent fetal distress in cases of sonographically proven fetal growth retardation.

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.