Most J, et al. - Researchers sought to describe changes in body composition during pregnancy in women with obesity via studying 54 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. In the second trimester, they observed lower gain in fat-free mass when compared with the third (2.7 ± 0.2 to 5.3 ± 0.2 kg), whereas there was decline in fat mass accumulation over time (0.6 ± 0.3 to −0.7 ± 0.4 kg). The fat mass gain in women with class 1 and 2 obesity during pregnancy was 1.1 ± 0.7 kg, whereas women with class 3 obesity lost 4.1 ± 0.6 kg fat mass. Only in the second trimester, obesity classes differ in fat accumulation. They observed a positive association of gestational weight gain with changes in plasma concentrations of insulin, leptin, and insulin resistance. These findings suggest a higher likelihood of preventing fat mass gain in the second trimester.