UNEXPECTED RELATIONSHIP BETWEEN FAT MASS AND BASAL METABOLIC-RATE IN PREGNANT-WOMEN

We investigated the relationships between BMR, fat-free mass (FFM) and fat mass in pregnancy, BMR was measured by indirect calorimetry and b ody composition was assessed by densitometry in seventeen non-pregnant women (79.9 (SD 26.3, range 50.5-151.4) kg) and sixteen pregnant wome n (75.7 (SD 20.6, range 54.5-115.9) kg). The pregnant women were evalu ated during weeks 31-35 of gestation, Multiple regression analysis of BMR with FFM and fat mass in the non-pregnant women showed that FFM wa s a highly significant predictor of BMR (P < 0.0001), but fat mass was not (P = 0.09). In contrast, in the pregnant women, multiple regressi on analysis revealed that fat mass was a highly significant predictor (P < 0.001), while FFM was not (P = 0.69). Evaluation of the interacti on terms in the combined data set confirmed that the relationships of BMR with FFM and fat mass differ significantly in non-pregnant and pre gnant women. It is proposed that pregnancy represents a unique conditi on during which BMR is regulated by maternal adipose reserves, An augm ented BMR in overweight pregnant women may be protective, given that e xcessive weight gain may be detrimental to neonatal and maternal healt h.