From pregnancy to breastfeeding: adequate maternal body mass index is essential to prevent a high body mass index in your children.

Objectives: To verify the associations between prenatal and perinatal factors with offspring body mass index (BMI) and the moderator role of maternal BMI in this relationship.

Methods: Cross-sectional study developed with 1,562 children and adolescents aged between 6 and 17 years, as well as their mothers, from southern Brazil. The prenatal and perinatal factors, weight, and height for the calculation of maternal BMI were self-reported. For the calculation of BMI, weight and height of the child/adolescent were measured on an anthropometric scale with a coupled stadiometer. Linear regression models were used for the moderation analysis. All analyzes were adjusted for the mother's and child's age, sex, sexual maturation, skin color/race, and educational level.

Results: cesarean as type of delivery (β=0.66; 95% CI=0.22 1.04; p=0.002) and pregnancy complications (β=0.60; 95% CI=0.15 1.04; p=0.002) were positively associated with offspring BMI. Schoolchildren who were breastfed for 4-6 months showed -0.56 kg/m² of BMI (95% CI=-1.06-0.06; p=0.02). Birth weight was also associated with BMI, with low weight being inversely (β=-0.59; 95% CI=-1.03-0.15; p=0.008), while overweight was positively related (β=0.84; 95% CI=0.08 1.60; p=0.02). The moderation analysis indicated a positive interaction between the mother's BMI and cesarean, pregnancy complications, and smoking with the offspring's BMI. On the other hand, there was an inverse association between breastfeeding from 7 to 12 months and the offspring BMI, only in mothers with high BMI.

Conclusions: Adequate maternal BMI is essential to prevent a high BMI in their children, especially when considering the influence of prenatal and perinatal risk factors.