Fetal growth retardation in rats from different levels of hypoxia.

Three groups of pregnant Wistar rats were subjected to 3 different levels of hypoxia: 11.6, 10.7 and 9.0%, respectively. Pair-fed and ad libitum fed control groups were included to control for the reduced food intake due to hypoxia. Within the range studied, fetal body weights decreased with decreased oxygen availability. Liver weights were more, brain weights less markedly reduced than body weights. Pair-fed but normally oxygenated animals showed slight reductions in body and organ weights compared to ad libitum fed controls. The fetuses subjected to hypoxia showed a placental hypertrophy relative to their body weights, while the least hypoxic fetuses showed an absolute placental hypertrophy. Placenta-fetal body ratios that were 150% greater than those observed in control animals were documented. In contrast, the fetuses of food-deprived animals were associated with abnormally small placentas.