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 intrauter ine growth restriction. STUDY DESIGN: Pregnant sheep underwent maternal catheterization at 88 to 93 days' gestation and fetal catheterization at 105-112 days' gestation. Twel ve pregnancies (group 1) provided control data (fetal Pao(2) 18-22 mm Hg), in 12 fetuses (group 2) mild hypoxemia (Pao(2) 16-19 mm Hg) was induced by prevention of the normal expansion of maternal blood volume, and in 7 fetus es (group 3) chronic hypoxemia (Pao(2) 12-18 mm Hg) developed spontaneously . RESULTS: In group 2 amniotic fluid osmolality and sodium concentrations wer e lower (approximately 30 mOsm/kg and 10 mEq/L, P < .05) and urea nitrogen revel was higher (10 mg/dL, P < .05) than in group 1. In group 3 osmolality and sodium concentrations at approximately 120 days' gestation were simila r to those in group 1.Whereas these values decreased with gestation in grou ps 1 and 2 (P < .05), they remained unchanged or increased in all fetuses i n group 3. Mortality rates in groups 1,2, and 3 were 1 of 12, 4 of 2 (diffe rence not significant), and 5 of 7 (P < .05), respectively. CONCLUSION: Absence of normal decrease in amniotic fluid osmolality with ge station, in association with a high perinatal mortality rate, was found in severely but not in mildly hypoxemic fetuses with intrauterine growth restr iction.