Maternal weight before pregnancy may shape toddlers’ development

By Pooja Toshniwal PahariaReviewed by Susha Cheriyedath, M.Sc.Apr 29 2026

A large Korean study links pre-pregnancy underweight and obesity to early developmental delays, while suggesting that risk may begin as early as the overweight range for cognitive development.

Study: Maternal pre-pregnancy BMI and neurodevelopmental outcomes in children aged 18–36 months: a nationwide cohort study in Korea. Image Credit: fast-stock / Shutterstock

A large population-based study from South Korea published in the journal Scientific Reports highlights that risks to early childhood development may extend beyond obesity alone.

Analyzing data from over 250,000 mother-child pairs, researchers found that maternal underweight and obesity were linked to higher risks across multiple developmental domains, while maternal overweight was associated particularly with increased cognitive delay at 18 to 24 months. 

Notably, the strongest effects were seen among children of severely obese mothers, with impacts spanning cognition, language, and self-care skills, underscoring the importance of preconception health for development during the first three years of life.

Maternal Pre-Pregnancy BMI and Child Development

Maternal pre-pregnancy weight plays a critical role in shaping both pregnancy outcomes and long-term child health. Obesity before conception increases the risk of complications such as preeclampsia, preterm birth, and cesarean delivery, while also predisposing offspring to cardiometabolic disorders and developmental challenges.

Emerging evidence links maternal body mass index (BMI) to early neurodevelopment, yet key questions remain.

The effects of maternal underweight are less clearly defined; findings across developmental domains are inconsistent, and most studies focus on Western populations. 

These gaps limit broader understanding and highlight the need for large, population-based analyses across diverse settings.

Korean Cohort Study Design and Methods

In this retrospective cohort study, researchers explored the influence of maternal pre-pregnancy body mass index (BMI) on early neurodevelopment among children in Korea.

The team analyzed data from 258,367 mother-child pairs drawn from the National Health Screening Program for Infants and Children (NHSPIC) and the National Health Insurance Service-Health Screening Cohort (NHIS-HEALS), including births during 2014-2021.

All children underwent the Korean Developmental Screening Test (K-DST) at two time points: 18 to 24 months and 30 to 36 months. The test evaluated six domains: gross and fine motor skills, cognition, language, sociality, and self-care.

The researchers classified maternal BMI according to Asia-Pacific criteria, based on health screening records obtained within the 3 years preceding delivery. They identified maternal comorbidities and clinical variables, including pregnancy-induced hypertension, diabetes, depression, and delivery method, using the International Classification of Diseases, Tenth Revision (ICD-10)-coded insurance claims data.

To reduce baseline differences between groups, the team used propensity score weighting via multivariable logistic regression. They then estimated the frequency of developmental delay and calculated relative risks (RRs) using generalized linear models, with children of normal-weight mothers used as the comparison group.

The analyses adjusted for multiple potential confounders. These included maternal age, birth characteristics, neonatal complications, and perinatal factors, but the observational design means the findings show associations rather than proving that maternal BMI directly caused developmental delays.

Maternal BMI and Toddler Neurodevelopment Findings

Among 258,367 mother-child pairs analyzed, 60% of mothers belonged to the healthy weight range, 12% underweight, 13% overweight, 12% obese, and 3% severely obese. As BMI increased, maternal comorbidities such as hypertension and diabetes became more common.

Depression, however, affected underweight, obese, and severely obese mothers more frequently. Higher maternal BMI also correlated with greater birth weight, increased neonatal intensive care admissions, and fewer vaginal deliveries.

By 18 to 24 months of age, children born to underweight mothers showed modestly increased risks of developmental delay, while those born to mothers with obesity, especially severe obesity, showed stronger elevations.

The strongest effects were observed in those born to mothers with severe obesity, where risks more than doubled for self-care (RR, 2.0) and nearly doubled for cognition (RR, 1.98), along with higher rates of language delay (RR, 1.5).

Interestingly, children of mothers in the overweight category also demonstrated elevated cognitive delays at this stage. By 30 to 36 months, the excess risk linked to low maternal weight had largely eased, suggesting partial developmental catch-up, while delays persisted among children exposed to maternal obesity, following a clear dose-response pattern across all assessed domains.

These findings point to distinct underlying mechanisms. Transient nutritional deficits in underweight mothers may support postnatal catch-up growth, whereas obesity-related inflammation, metabolic disruption, and hormonal imbalance are likely to exert longer-lasting effects on the developing brain.

Together, the results reinforce growing evidence that maternal weight, particularly excess weight, is associated with early neurodevelopmental differences that may persist into toddlerhood, although residual confounding from socioeconomic, educational, genetic, home, and postnatal factors cannot be excluded.

Preconception Weight and Public Health Implications

These findings push the conversation beyond obesity, suggesting that neurodevelopmental risk may begin as early as the overweight range, particularly for cognitive delay in early toddlerhood. This has immediate clinical and public health implications.

Routine BMI screening and targeted preconception counseling should extend to women across the full weight spectrum, not only those with obesity. Early identification of at-risk mother-child pairs could enable timely monitoring and intervention during critical developmental windows.

Looking ahead, more precise modeling approaches and longitudinal studies are needed to define optimal BMI ranges and track developmental trajectories over time. Integrating gestational, socioeconomic, and postnatal factors will further refine risk assessment.

The authors also noted important limitations, including reliance on developmental screening rather than comprehensive clinical diagnosis, the absence of gestational weight gain data, BMI’s inability to capture body composition or micronutrient status, and possible selection bias because the final cohort represented only a subset of all births during the study period.

As rates of overweight and obesity continue to rise globally, these insights offer a crucial opportunity to shift prevention strategies earlier, before pregnancy begins, potentially improving neurodevelopmental outcomes at a population level, with lasting benefits for future generations.