This study was conducted to determine whether brief, intermittent exposure to hypoxia with little change in nutrient intake would affect fetal growth. Pregnant rats were exposed to 1 or 2 h of hypoxia (FiO₂ = 0.09–0.095) from days 15 to 19 of gestation. Exposure to 1 h of hypoxia decreased fetal body weight and length, liver weight and increased the brain/liver weight ratio (p < 0.05) as compared to controls. Two hours of hypoxia decreased fetal body weight and length, and heart, lung, kidney, gut, brain and liver weights (p < 0.01), but did not affect the brain/liver weight ratio. Two hours of hypoxia decreased maternal food intake and weight gain (p < 0.05), but fetal growth was not significantly altered in pair-fed controls. These data demonstrate that brief, intermittent periods of intrauterine hypoxia have significant effects on fetal growth.

Bilateral nephrectomy retards fetal growth and decreases somatomedin (insulin-like growth factor-I, IGF-I) activity. To determine whether nephrectomy alters the synthesis of IGF-I or its binding proteins (IGFBPs), we studied 6 sets of twin fetuses. Kidneys were removed bilaterally from 1 twin of each set at 112–122 days of gestation (term 145 days). Plasma IGF-I concentrations were greater in nephrectomized fetuses than in the intact twins during the 1st week (261 ± 35 vs. 153 ± 21 ng/ml, p < 0.02; mean ± SE) but not the 2nd week after surgery. Nephrectomy increased the abundance of the IGFBPs to levels 2–3 times greater than those in intact twins. Fetal hepatic IGFBP1 mRNA levels increased in 4 of 6 nephrectomized fetuses, while those of IGF-I, IGF-II, IGFBP2 were unchanged. Nephrectomy markedly alters the abundance of IGF-I and IGFBPs in plasma probably through mechanisms unrelated to synthesis.