A large study from South Korea found that low pre-pregnancy weight and obesity were associated with early developmental delays, suggesting that risk may begin in the overweight range for cognitive development.
Study: Maternal pre-pregnancy BMI and child neurodevelopmental outcomes between 18 and 36 months of age: a national cohort study in South Korea. Image credit: fast-stock / Shutterstock
Large-scale Korean population-based study published in journal scientific report It highlights that risks to early childhood development may extend beyond obesity.
After analyzing data from more than 250,000 mother-infant pairs, researchers found that maternal underweight and obesity were associated with increased risk across multiple developmental domains, with maternal overweight specifically associated with increased cognitive delays between 18 and 24 months of age.
In particular, the strongest effects were seen in children of severely obese mothers, with effects extending to cognition, language and self-care skills, highlighting the importance of preconception health in the first three years of life.
Maternal pre-pregnancy BMI and child growth
A mother’s pre-pregnancy weight plays an important role in shaping both the pregnancy outcome and the child’s long-term health. Obesity before pregnancy increases the risk of complications such as preeclampsia, preterm birth, and caesarean section, while predisposing offspring to cardiometabolic disorders and developmental challenges.
Emerging evidence links maternal body mass index (BMI) and early neurodevelopment, but important questions remain.
The effects of maternal low birth weight are less clearly defined. Findings across developmental domains are inconsistent, with most studies focusing on Western populations.
These gaps limit widespread understanding and highlight the need for large-scale population-based analyzes across diverse settings.
Korean cohort study design and methods
In this retrospective cohort study, researchers investigated the influence of mothers’ pre-pregnancy body mass index (BMI) on the early neurodevelopment of their Korean children.
The research team analyzed data on 258,367 mother-infant pairs drawn from the National Infant Health Examination Program (NHSPIC) and the National Health Insurance Service Health Examination Cohort (NHIS-HEALS), including births from 2014 to 2021.
All children underwent the Korean Developmental Screening Test (K-DST) at two time points: 18–24 months of age and 30–36 months of age. The test assessed six areas: gross and fine motor skills, cognition, language, social skills, and self-care.
The researchers classified maternal BMI according to Asia-Pacific standards based on health examination records obtained within three years before birth. They used International Classification of Diseases, 10th Revision (ICD-10) coded insurance claims data to identify maternal comorbidities and clinical variables, including gestational hypertension, diabetes, depression, and mode of delivery.
To reduce baseline differences between groups, the team used propensity score weighting with multivariable logistic regression. Using children of normal weight mothers as a comparison group, we then used generalized linear models to estimate the frequency of developmental delay and calculate relative risks (RRs).
Analyzes were adjusted to account for multiple potential confounders. These include maternal age, birth characteristics, neonatal complications, and perinatal factors, but the observational design means the results show an association rather than proving that maternal BMI directly causes developmental delay.
Findings on maternal BMI and infant neurodevelopment
Of the 258,367 mother-child pairs analyzed, 60% of mothers were in the healthy weight range, 12% were underweight, 13% were overweight, 12% were obese, and 3% were severely obese. As BMI increased, comorbidities such as maternal hypertension and diabetes became more common.
However, mothers who were underweight, obese, or severely obese were more likely to experience depression. Higher maternal BMI was also associated with higher birth weight, increased neonatal intensive care admissions, and fewer vaginal deliveries.
By 18 to 24 months of age, children born to mothers with low birth weight were shown to have a slightly increased risk of developmental delays, but children born to mothers who were obese, particularly severely obese, had a stronger increased risk.
The strongest effects were observed in offspring of severely obese mothers, who had more than double the risk for self-care (RR, 2.0), nearly double the risk for cognition (RR, 1.98), and higher rates of language delay (RR, 1.5).
Interestingly, children of mothers in the overweight category also showed increased cognitive delay at this stage. By 30–36 months, the excess risk associated with maternal underweight was significantly reduced, suggesting partial developmental catch-up, whereas the delay persisted in children exposed to maternal obesity and followed a clear dose-response pattern across all domains assessed.
These findings indicate that the underlying mechanisms are different. Temporary nutritional deficiencies in low birth weight mothers may help restore postnatal growth, but obesity-related inflammation, metabolic disruption, and hormonal imbalances can have long-term effects on the developing brain.
Together, these results support growing evidence that maternal weight, particularly excess weight, is associated with early neurodevelopmental differences that may persist into early childhood, although residual confounding by socioeconomic, educational, genetic, family, and postnatal factors cannot be excluded.
Pre-pregnancy weight and public health implications
These findings push the discussion beyond obesity and suggest that neurodevelopmental risks may begin in the overweight range, particularly with regard to cognitive delays in early childhood. This has immediate clinical and public health implications.
Regular BMI screening and targeted preconception counseling should be extended to women across the entire weight range, not just those with obesity. Early identification of at-risk mother-infant pairs may allow for timely monitoring and intervention during critical developmental periods.
Looking forward, more precise modeling approaches and longitudinal studies are needed to define optimal BMI ranges and track developmental trajectories over time. Integrating pregnancy, socio-economic, and postpartum factors further refines risk assessment.
The authors also noted important limitations, including reliance on developmental screening rather than comprehensive clinical diagnosis, lack of gestational weight gain data, inability of BMI to capture body composition or micronutrient status, and potential for selection bias as the final cohort represented only a subset of all births during the study period.
As overweight and obesity rates continue to rise globally, these insights provide important opportunities to modify prevention strategies early, before pregnancy begins, potentially improving neurodevelopmental outcomes at the population level and providing lasting benefits for future generations.
Reference magazines:
- Shin, J., Kim, T.E., Park, S.H., et al. (2026). Prepregnancy BMI and neurodevelopmental outcomes in children aged 18 to 36 months: a national cohort study in South Korea. scientific report, Doi: https://doi.org/10.1038/s41598-026-51035-7
