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Background: The rising prevalence of pediatric obesity is a critical public health issue linked to lifelong metabolic and cardiovascular risks. Identifying early-life predictors is essential for effective prevention.

Aim: This thesis aimed to identify pre- and perinatal factors associated with early childhood growth and the development of overweight and obesity.

Methods: Four studies were conducted using the Uppsala County Mother and Child (UCMC) cohort, including up to 57,000 mother-child pairs born between 2000 and 2015. Data were integrated from several Swedish national registers. Study I examined maternal random capillary glucose levels; Study II investigated maternal pre-pregnancy BMI and gestational weight gain (GWG); Study III compared elective Caesarean section (CS) with vaginal delivery using propensity score matching; and Study IV evaluated the interaction between birth size (Large-for-Gestational-Age, LGA) and infancy growth patterns (0–1.5 years). Analyses included mixed regression models for growth trajectories and logistic and Poisson regression for overweight and obesity risk.

Results: Higher maternal glucose levels were associated with increased birth size, though these effects diminished by age five (Study I). In contrast, maternal pre-pregnancy BMI and excessive GWG were strongly associated with size at birth and sustained higher BMI trajectories and increased odds of childhood obesity at age four. While GWG significantly influenced growth up to 18 months maternal pre-pregnancy BMI emerged as the dominant factor for growth between 1.5 and 5 years (Study II). Mode of delivery did not significantly influence growth trajectories or obesity risk when adjusted for baseline characteristics (Study III). Study IV revealed that children born LGA with accelerated infancy growth faced the highest risk of obesity (RR ~5.0–7.9). Children born Appropriate-for-Gestational-Age (AGA) who experienced accelerated infancy growth had a higher risk of obesity than children born LGA who experienced decelerated infancy growth.

Conclusions: Prenatal and early postnatal factors are significant predictors of childhood adiposity. While elective CS does not appear to increase risk, maternal BMI and GWG, maternal glucose levels, and infancy growth velocity are critical markers. These findings can help refine child healthcare guidelines to mitigate the long-term adverse health outcomes associated with accelerated BMI trajectories.