LONGITUDINAL CHANGES IN BODY-COMPOSITION AND ENERGY-BALANCE IN LEAN WOMEN WITH NORMAL AND ABNORMAL GLUCOSE-TOLERANCE DURING PREGNANCY

OBJECTIVE: The objective of this study was to evaluate the longitudina l changes in energy expenditure and body composition in relationship t o alterations in carbohydrate metabolism in women with normal and abno rmal glucose metabolism. We hypothesized that women with decreased ins ulin sensitivity before conception would have less fat accretion and s maller increases in energy expenditure. STUDY DESIGN: Six women with n ormal glucose tolerance and 10 women with abnormal glucose tolerance w ere evaluated before conception, and in early (12 to 14 weeks) and lat e (34 to 36 weeks) gestation. Body composition was estimated by hydrod ensitometry, resting energy expenditure, and glucose and fat metabolis m by indirect calorimetry, endogenous glucose production by infusion o f [6-6 H-2(2)] glucose, and insulin sensitivity using a hyperinsulinem ic-euglycemic clamp (40 mU/m(2)/min). RESULTS: There was a smaller inc rease in fat mass (1.3 kg [P = .04]) in early pregnancy in women with abnormal glucose tolerance before pregnancy. Indirect calorimetry meas ured gestational age-related increases in basal oxygen utilization, wi th or without correction for fat-free mass ((V)over dot O-2, P = .002) , resting energy expenditure (expressed in kilocalories, P = .0001), a nd carbohydrate oxidation (P = .0003). The insulin-mediated elevation in (V)over dot O-2 increased in later gestation (V)over dot O-2 (P = . 005), as did resting energy expenditure (P = .0001) and fat oxidation (P = 0.0001). However, there was a decrease in respiratory quotient (P = .0001), carbohydrate oxidation (P = .002), and nonoxidative carbohy drate metabolism (P = .0001) with advancing gestation during insulin i nfusion. in early pregnancy, changes in fat mass correlated inversely with changes in insulin sensitivity (r = -0.52, P = .04) and changes i n basal (V)over dot O-2 correlated inversely with decreases in basal e ndogenous glucose production (r = -0.74, P = .01). CONCLUSION: In earl y gestation, the changes in maternal fat mass and basal oxygen consump tion are inversely related to the changes in insulin sensitivity. This response in lean women with decreased insulin sensitivity before conc eption may have survival value by providing a larger amount of availab le substrate to meet fetoplacental needs during gestation.