Prepregnancy body mass index influences lipid oxidation rate during pregnancy

The influence of maternal body mass index (BMI) on respiratory quotient during pregnancy is not clear. We aim to evaluate longitudinal changes in energy expenditure, respiratory quotient, and substrate oxidation rates in normal and overweight women with uncomplicated pregnancies. We hypothesized that the threshold period in switching from a predominantly carbohydrate to a predominantly lipid metabolism may be different in normal and overweight women.

Forty healthy pregnant women were recruited for a prospective cohort study. They were divided into two groups, normal and overweight (BMI <25 kg/m² or ≥25 kg/m² ). Comparisons of indirect calorimetry data were performed monthly throughout pregnancy. The relationships between energy and substrate metabolism variables and maternal BMI were also analyzed.

There was a significant increase in oxygen consumption (Vo₂ ), carbon dioxide production (Vco₂ ) and resting energy expenditure during pregnancy in both normal and overweight women. In the normal weight group, respiratory quotient decreased during the second trimester and increased in the last trimester. Respiratory quotient was lower in the overweight group in the second trimester and decreased in the last trimester; between-group differences being significant at 20 and 36 weeks (0.85 ± 0.06 vs. 0.81 ± 0.01, p = 0.009; 0.87 ± 0.05 vs. 0.80 ± 0.03, p = 0.01, respectively). Lipid oxidation was significantly higher in overweight women at both 20 and 36 weeks (36.8 ± 19.7% vs. 55.2 ± 5.6%, p = 0.003 and 33.6 ± 18.2% vs. 59.6 ± 12.7%, p = 0.007, for normal and overweight group, respectively).

Prepregnancy maternal BMI influences lipid oxidation rate and respiratory quotient during pregnancy.