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 body mass index (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 (β = -0.02 kg; 95% CI -0.03, -0.01). Pre-pregnancy overweight women experienced an increase in all body components (BF: β = 4.91%, 95% CI 3.79, 6.04; FM: β = 6.46 kg, 95% CI 5.26, 7.67; FFM: β = 3.72 kg, 95% CI 2.80, 4.65) and BMI (β = 4.51 kg/m², 95% CI 3.91, 5.12). Multiparous women showed BMI increases (β = 0.76 kg/m², 95% CI 0.11, 1.41), and those who delivered by caesarean had FFM (β = 1.87 kg, 95% CI 0.67, 3.07) and BMI (β = 1.39 kg/m², 95% CI 0.61, 2.18) increases. Women who birthed girls had reductions in FM (β = -1.24 kg, 95% CI -2.41, -0.07) and FFM (β = -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.

Keywords: lactation; maternal BMI; maternal body composition; postpartum period; prospective study.

怀孕和哺乳会改变女性的身体组成（BC），但很少有纵向研究调查产后身体组成的轨迹。我们的目标是探讨母亲和婴儿的预测因素对哺乳期间母亲体脂（BF）、脂肪质量（FM）、去脂体重（FFM）和体质指数（BMI）轨迹的影响。这项纵向研究跟踪了234对巴西母子，分别在产后1.0-3.49个月、3.5-5.99个月和6.0-8.5个月内进行随访。母亲的身体组成是在所有随访点使用生物电阻抗法估算的。采用具有时间（产后周数）交互项的纵向混合效应模型。去脂体重在产后周数内显著下降（β = -0.02 kg；95% CI -0.03，-0.01）。孕前超重女性的所有身体组成成分均有所增加（BF：β = 4.91%，95% CI 3.79，6.04；FM：β = 6.46 kg，95% CI 5.26，7.67；FFM：β = 3.72 kg，95% CI 2.80，4.65）和BMI（β = 4.51 kg/m²，95% CI 3.91，5.12）。多胎次女性的BMI有所增加（β = 0.76 kg/m²，95% CI 0.11，1.41），而剖宫产分娩的女性去脂体重和BMI均有增加（FFM：β = 1.87 kg，95% CI 0.67，3.07；BMI：β = 1.39 kg/m²，95% CI 0.61，2.18）。分娩女孩的女性脂肪质量和去脂体重有所减少（FM：β = -1.24 kg，95% CI -2.41，-0.07；FFM：β = -0.93 kg，95% CI -1.84，-0.01）。母亲年龄≥30岁、家庭收入较高、多胎次和婴儿性别之间存在身体组成和BMI轨迹的交互作用。母亲年龄、孕前BMI、生育次数、家庭收入、分娩方式和婴儿性别预测母亲的身体组成和BMI变化轨迹。

关键词：哺乳；母亲BMI；母亲身体构成；产后时期；前瞻性研究。