Amniotic fluid composition in the fetal lamb with intrauterine growth restriction

OBJECTIVE: Our aim was to examine changes from normal in the composition of amniotic fluid in fetal lambs with mild and severe hypoxemia and intrauterine growth restriction. STUDY DESIGN: Pregnant sheep underwent maternal catheterization at 88 to 93 days' gestation and fetal catheterization at 105-112 days' gestation. Twelve pregnancies (group 1) provided control data (fetal PaO₂ 18-22 mm Hg), in 12 fetuses (group 2) mild hypoxemia (PaO₂ 16-19 mm Hg) was induced by prevention of the normal expansion of maternal blood volume, and in 7 fetuses (group 3) chronic hypoxemia (PaO₂ 12-18 mm Hg) developed spontaneously. RESULTS: In group 2 amniotic fluid osmolality and sodium concentrations were lower (approximately 30 mOsm/kg and 10 mEq/L, P < .05) and urea nitrogen level was higher (10 mg/dL, P < .05) than in group 1, in group 3 osmolality and sodium concentrations at approximately 120 days' gestation were similar to those in group 1. Whereas these values decreased with gestation n groups 1 and 2 (P < .05), they remained unchanged or increased in all fetuses in group 3. Mortality rates in groups 1,2, and 3 were 1 of 12, 4 of 12 (difference not significant), and 5 of 7 (P < .05), respectively. CONCLUSION: Absence of normal decrease in amniotic fluid osmolality with gestation, in association with a high perinatal mortality rate, was found in severely but not in mildly hypoxemic fetuses with intrauterine growth restriction.