• Insulin sensitivity;
  • Postprandial thermogenesis;
  • Pregnancy

Insulin sensitivity and postprandial thermogenesis were investigated at various stages of pregnancy to assess if changes in insulin sensitivity contribute to energy conservation during pregnancy. Cross-sectional and longitudinal studies were undertaken. Sixteen control non-pregnant women were compared with 10 women in the second trimester (2nd) and thirteen women in the third trimester (3rd) of uncomplicated pregnancy. Six women were studied at all three time points. The slope of plasma glucose decline following a bolus of intravenous insulin was used as an index of insulin sensitivity. Resting energy expenditure was measured with continuous indirect calorimetry. Postprandial thermogenesis was measured as the change in energy expenditure for the 2 h after a mixed meal. Results are expressed as mean ± SEM or median (interquartile range). Insulin sensitivity was lower as pregnancy progressed (non-pregnant control 181 (177–205) vs 2nd 111 (100–112) vs 3rd 96 (80–109) μmol l−1 min−1, p < 0.001). Fasting insulin levels were significantly higher in the third trimester but not in the second trimester (non-pregnant control 1.9 (1.5–6.0) vs 2nd 3.1 (2.8–5.2) vs 3rd 8.6 (4.8–9.7) mU l−1, p < 0.05). Meal stimulated insulin levels were higher in the second and third trimesters compared to non-pregnant women (insulin area over 2 h, postmeal, non-pregnant control 78 ± 10 vs 2nd 92 ± 14 vs 3rd 145 ± 14 mU l−1 h−1, p < 0.005). Postprandial thermogenesis was lowest in the third trimester (non-pregnant control 103 ± 5 vs 2nd 74 ± 8 vs 3rd 48 ± 8 kJ, p < 0.01). In pregnancy insulin sensitivity correlated positively with postprandial thermogenesis (r = +0.57 p < 0.02). Insulin insensitivity is present in the second trimester and increases in the third trimester of normal pregnancy. Postprandial thermogenesis is reduced in pregnancy and correlates positively with insulin sensitivity. Insulin insensitivity may play an important physiological role in limiting the energy demands of pregnancy.