Objective To compare plasma glucose in pregnant women living at very high altitude; pregnant women living at sea level; non-pregnant women living at very high altitude; and non-pregnant women living at sea level.Design Cross-sectional study. Participants Ninety-four pregnant women attending for routine antenatal care at 8±42 weeks of gestation in Cerro de Pasco, Peru which is situated 4370 m above sea level; 122 pregnant women in Lima, which is at sea level; 22 non-pregnant women in Cerro de Pasco; and 31 non-pregnant women in Lima. Methods Plasma glucose concentrations were measured in samples obtained from the antecubital vein between 8 am and 10 am after an overnight period of fasting for at least 10 hours. Results Fasting plasma glucose was lower in women at high altitude than in those at sea level, and in both groups the level was lower in pregnant women than in non-pregnant controls. The body mass index was not signi®-cantly different between all four groups, and it did not have a signi®cant independent contribution in explaining the variance in fasting plasma glucose.Conclusion Women native at high altitude have lower plasma glucose concentrations before and during pregnancy than those at sea level.

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