Previous studies have shown that prolonged exposure to hypoxia during pregnancy results in fetal growth retardation due either to a limitation of fetal oxygen supply or reduced maternal nutrient intake secondary to appetite suppression. The purpose of this study was to determine whether daily exposure to brief episodes of hypoxia during the last trimester of gestation would have lasting effects on fetal growth. Pregnant Sprague-Dawley rats were exposed to one (H1, n=8) or two (H2, n=10) hours per day of hypoxia (F1O2 9-10%) from days 15-19 of gestation. These groups were matched to controls who breathed room air (C1, n=8; C2, n=10). All animals had free access to rat chow and water. On day 20 dams were weighed, daily food intake calculated and individual fetal organ weights recorded. Table

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Daily exposure to one hour of hypoxia decreased fetal body weight, length and liver weight, did not affect fetal brain weight and increased brain/liver weight ratio as compared to controls. This amount of hypoxia did not alter maternal weight gain or food intake (Food). Daily exposure to two hours of hypoxia decreased fetal body weight, length and liver weight as well as brain, heart, lung, kidney and gut weights (5-15% decrease p<0.05). In addition, two hours of hypoxia decreased maternal food intake and weight gain(p<0.05). Thus, 1h of hypoxia per day is sufficient to reduce fetal growth with no effect on brain weight. Two h of hypoxia per day has a more deleterious effect on fetal growth; this may be due to a reduction in fetal oxygen supply and/or maternal food intake. These data demonstrate that brief, daily exposure to hypoxia during the last trimester can seriously affect fetal growth. Similar mechanisms may be responsible for some cases of growth retardation in infants following repeated episodes of intrauterine hypoxia resulting from strenuous maternal exercise, umbilical cord compression or uterine blood flow reduction. Supported by NIH and AHA.