Predictors of longitudinal changes in body composition and BMI in Brazilian lactating women during the first 8·5 months postpartum

Pregnancy and lactation change women's body composition (BC), but few longitudinal studies have investigated postpartum BC trajectories. We aimed to investigate maternal and infant predictors of maternal body fat (BF), fat mass (FM), fat-free mass (FFM) and BMI trajectories during lactation. Longitudinal study with 234 Brazilian mother-infant dyads followed at 1·0-3·49, 3·5-5·99 and 6·0-8·5 months postpartum. Maternal BC was estimated using bioelectrical impedance at all follow-up points. Longitudinal mixed-effects models with interaction terms with time (weeks postpartum) were employed. FFM declined significantly over weeks postpartum (<i>β</i> = -0·02 kg; 95 % CI -0·03, -0·01). Pre-pregnancy overweight women experienced an increase in all body components (BF: <i>β</i> = 4·91 %, 95 % CI 3·79, 6·04; FM: <i>β</i> = 6·46 kg, 95 % CI 5·26, 7·67; FFM: <i>β</i> = 3·72 kg, 95 % CI 2·80, 4·65) and BMI (<i>β</i> = 4·51 kg/m², 95 % CI 3·91, 5·12). Multiparous women showed BMI increases (<i>β</i> = 0·76 kg/m², 95 % CI 0·11, 1·41), and those who delivered by caesarean had FFM (<i>β</i> = 1·87 kg, 95 % CI 0·67, 3·07) and BMI (<i>β</i> = 1·39 kg/m², 95 % CI 0·61, 2·18) increases. Women who birthed girls had reductions in FM (<i>β</i> = -1·24 kg, 95 % CI -2·41, -0·07) and FFM (<i>β</i> = -0·93 kg, 95 % CI -1·84, -0·01). Interactions occurred between maternal age ≥ 30 years, higher family income, multiparity and infant sex for BC and BMI trajectories. Maternal age, pre-pregnancy BMI, parity, family income, mode of delivery and infant sex predict maternal BC and BMI trajectories.