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Summary: The objective of the study was to measure energy metabolism and body composition during pregnancy and postpartum, compared to non-pregnant women, using non-invasive techniques. A longitudinal study of eight normotensive pregnant women was carried out at 19 ± 1 and 36 ± 1 weeks gestation, and postpartum. A cross-sectional study was also performed comparing postpartum to 12 nonpregnant women. Indirect calorimetry was performed while fasting to measure basal metabolic rate (BMR) and postprandially to measure diet-induced thermogenesis (DIT). Body composition consists of fat mass, lean body mass (LBM), and total body water (TBW) and was measured by bio-electrical impedance. Insulin resistance was indirectly assessed by glucose and insulin concentration and DIT. Weight gain in pregnancy was predominantly fat mass (p < 0.01), but LBM and TBW also increased (p < 0.01). Weight loss postpartum was comprised of fat mass, LBM and TBW (p < 0.01). BMR, glucose and insulin increased in pregnancy and decreased postpartum (p < 0.05), but DIT was unchanged. The BMR was not correlated with weight gain. Apart from fat mass, postpartum and non-pregnant women were similar. The insulin resistance increased insulin and glucose levels but not DIT. Fat mass was the major component of weight gain during pregnancy and there was an increase in BMR, glucose and insulin but no change in DIT. BMR decreased to normal but fat mass remained elevated 16 weeks post-partum.