THE EFFECTS OF 24 HOURS OF REDUCED UTERINE BLOOD-FLOW ON FETAL FLUID BALANCE IN SHEEP

OBJECTIVE: Our aim was to determine the effects of a sustained reducti on in uteroplacental perfusion, leading to fetal hypoxia, on determina nts of amniotic fluid Volume in sheep. STUDY DESIGN: Surgery was perfo rmed on five pregnant ewes 110 to 116 days after mating. At 127.3 +/- 2.2 days uterine blood flaw was reduced for 24 hours, which reduced fe tal Sao(2) from 61.9% +/- 1.2% to 24.9% +/- 0.8%. RESULTS: Fetal urine production was increased from a control value of 193.0 +/- 24.0 ml/kg per 24 hours to 279.3 +/- 30.0 ml/kg per 24 hours during periods of r educed uterine blood flow and remained above control values for up to 48 hours after the reduced uterine blood flow period. A substantial lo ss of fetal water and electrolytes occurred through urine, which was a ssociated with changes in the composition of fetal plasma and fetal tr acheal, fetal swallowed, and amniotic fluids. Fetal swallowing was red uced throughout the reduced uterine blood flow period from a control v alue of 200.8 +/- 56.0 ml/kg per 24 hours to 32.7 +/- 8.4 ml/kg per 24 hours and returned to control levels after the cessation of the reduc ed uterine blood flow. CONCLUSION: We conclude that 24 hours of reduce d uterine blood flow causes major changes in fetal renal function and fetal swallowing that, in spite of an expected reduction in lung liqui d production, would increase the flow of fluid and electrolytes from t he fetus into the amniotic sac.