Body Composition During Pregnancy Differs by Obesity Class

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.