Body Composition During Pregnancy Differs by Obesity Class

Abstract

Objective: The aim of this study is to characterize changes in body composition during pregnancy in women with obesity.

Methods: Fifty-four healthy women with obesity (class 1, 30-34.9 kg/m² : n = 25; class 2, 35-39.9 kg/m² : n = 21; class 3, ≥ 40.0 kg/m² : n = 8) expecting a singleton pregnancy were studied. Body composition was measured in early pregnancy (13-16 weeks), midpregnancy (24-27 weeks), and late pregnancy (35-37 weeks) using air displacement plethysmography, stable isotopes, and skinfold thickness measurements. Fasting glucose, insulin, and leptin were measured.

Results: The gain in fat-free mass was lower in the second trimester compared with the third (2.7 ± 0.2 to 5.3 ± 0.2 kg; P < 0.001), whereas fat mass accumulation declined over time (0.6 ± 0.3 to -0.7 ± 0.4 kg; P = 0.005). Women with class 1 and 2 obesity gained 1.1 ± 0.7 kg of fat mass during pregnancy, while women with class 3 obesity lost 4.1 ± 0.6 kg (both P < 0.001). The difference in fat accumulation between obesity classes was observed only in the second trimester (P = 0.02). Gestational weight gain was associated positively with changes in plasma concentrations of insulin, leptin, and insulin resistance (all P < 0.01).

Conclusions: Gestational weight gain in pregnancy differs by obesity class and trimester. Women with class 3 obesity gain less body weight and fat mass. Fat mass gain is most likely preventable in the second trimester.

Figure 1.. Enrollment BMI Distribution, Gestational Weight Gain and its Components

Women with class 1, 2 and 3 obesity are presented in white, grey and black, respectively. Data is presented as frequency (A), individual data points (B-F), and as mean±SEM (G). (A) Enrollment BMI was assessed <15 weeks gestation. (B-F) Linear regressions were performed to assess associations between enrollment BMI and change in body weight (B), fat mass (c), fat-free mass (D), water (E) and fetal size (F). Body composition was measured using air displacement plethysmography, doubly-labelled water, and fetal weight by 3D-ultrasound.

Figure 2.. Components of Gestational Weight Gain by Trimester

Women were classified as class 1, 2 and 3 obesity at enrollment (<15 weeks gestation). Data is presented as mean±SEM. The average change in body weight (white circles) and its components (stacked bars) was assessed from early pregnancy (14.9±0.1 weeks) to mid-pregnancy (25.1±0.1 weeks) and late pregnancy (35.9±0.1 weeks). Body composition was measured using air displacement plethysmography, doubly-labelled water, and fetal weight by 3D-ultrasound. Total body water accumulation at 24–27 weeks was estimated using hydration constant measured at 35–37 weeks. For statistical analysis, see Table 2.

Figure 3.. Changes in Metabolic Biomarkers in Obese Pregnancy and the Relationship with Gestational Weight and Fat Mass

Women were classified as obesity class 1 (white circles), 2 (grey circles) and 3 (black circles) at enrollment (<15 weeks gestation). Data is presented as mean±SEM. Plasma concentrations were assessed in early pregnancy (Visit 1, 14.9±0.1 weeks), mid-pregnancy (Visit 2, 25.1±0.1 weeks) and late pregnancy (Visit 3, 35.9±0.1 weeks). Panels A, C, E and G show the measured plasma concentration at each visit; panels B, D, F and H show the associations between fat accumulation during pregnancy and the change in plasma concentrations as percent change from early to late pregnancy. Statistical significance of the difference between obesity classes in early pregnancy is indicated as *, if P<0.05. Linear regression were used to assess the association between weight gain and changes in plasma concentrations.