OBJECTIVE: Maternal health behavior influences offspring health and obesity risk. This study examined the long-term effects of an antenatal lifestyle intervention on somatic growth and neurodevelopment of preschool-aged children. METHODS: We followed children born to women in the cluster-randomized GeliS trial who received usual care (CG) or lifestyle counseling (IG). Anthropometrics and neurodevelopment data for children aged 4 and 5 were collected from routine health examinations and the Ages-and-Stages Questionnaire (ASQ). RESULTS: Of 2 286 women initially enrolled, 1 403 reported on their child's development. The intervention had no effect on weight, height, head circumference, BMI, or percentiles and z-scores at ages 4 and 5. In IG compared to CG, the proportion of children with underweight was lower (4 years: 7.8% vs. 10.9%
5 years: 8.1% vs. 8.9%), while overweight (4 years: 6.5% vs. 4.2%
5 years: 5.1% vs. 3.4%) and obesity proportions (4 years: 1.0% vs. 1.1%
5 years: 2.7% vs. 1.6%) were higher. IG children were more likely to fall into a higher weight category at 4 (p = 0.017) and 5 years (p = 0.075). ASQ scores were similar across both groups. CONCLUSION: Despite slight weight differences, the pregnancy lifestyle intervention had no meaningful impact on child somatic growth or neurodevelopment up to age 5. IMPACT: This comprehensive antenatal lifestyle intervention, executed as a large-scale real-world effectiveness trial, did not demonstrate any long-term effect on children's anthropometry or their risk of overweight or obesity up to 5 years of age. No discernible intervention effects were observed concerning children's neurodevelopment outcomes. Personalized antenatal interventions targeting the individual risk profiles of pregnant women may be needed to substantially modify lifestyle behaviors and achieve sustainable impacts on child development and obesity risk.