Two-Thirds of Pregnancies Have Weight Gain Outside Recommended Ranges, Meta-Analysis of 1.6 Million Women Finds

A new systematic review and meta-analysis published in The BMJ has found that approximately two-thirds (68%) of pregnancies involve gestational weight gain (GWG) that is either above or below current recommendations. The analysis, which included data from over 1.6 million women, establishes a clear link between non-recommended weight gain and an increased risk of adverse maternal and neonatal outcomes, including preterm birth, caesarean delivery, and admission to a neonatal intensive care unit.

Breakdown of Key Findings

The study quantifies the specific health risks for both mother and baby when gestational weight gain falls outside the recommended ranges. These risks differ significantly depending on whether weight gain is insufficient or excessive, and vary further based on a woman's pre-pregnancy body mass index (BMI).

Risks Associated with GWG Below Recommendations

Gaining too little weight was most strongly linked to the baby being born too early or too small, increasing risks for preterm birth, low birth weight, and respiratory distress. However, this risk profile varied across BMI categories; the higher risk of preterm birth was most pronounced in underweight and normal-weight women, while the protective effect against caesarean delivery was only statistically significant for those in the overweight and obese categories.

Risks Associated with GWG Above Recommendations

Conversely, gaining too much weight was associated with a higher likelihood of delivery complications, hypertensive disorders, and larger infants requiring more intensive care. The analysis showed that while the increased risk for hypertensive disorders of pregnancy was significant for normal weight, overweight, and obese women, it was not for those who were underweight before pregnancy. In contrast, the risk of having a large-for-gestational-age infant was consistently elevated across all BMI categories.

Implications for Global Pregnancy Guidelines

These findings are particularly significant because most countries currently rely on the Institute of Medicine (IOM) guidelines, which are based on data from predominantly white women in high-income countries from the 1980s. These decades-old guidelines, based on a less diverse population from a different era, are poorly matched to the realities of global public health today, where maternal age and BMI are steadily rising.

In response to this gap, the World Health Organization (WHO) has initiated a process to develop new, global standards for healthy GWG. The study's authors state that their work is intended to support this global initiative.

"Our findings inform and support the need for optimised, evidence based WHO international GWG reference standards based on individual patient data, applicable across the full BMI range in contemporary and diverse global populations. This will build on and improve current recommendations and are essential to underpin multi level support to improve the health of mothers and babies worldwide.”

A Call for a Nuanced Clinical Approach

This significant variation in risk across BMI categories is precisely why a linked editorial by Dr. Annick Bogaerts and Dr. Dominika Osicka argues that the findings challenge the "black and white logic" of current clinical guidelines. They suggest that rather than warning all women against exceeding fixed cut-offs, a more nuanced approach is needed, with a focus on patterns of weight gain, its underlying determinants, and personalized, non-punitive counseling.

They conclude with a call for broader public health action:

“Without comprehensive, life course public health strategies, the obesity epidemic will continue across generations. Governments and (inter)national agencies must act now to support women’s health before, during, and after pregnancy, ensuring that the next generation inherits the opportunity not the risk.”

Study Methodology and Limitations

The research was a systematic review and meta-analysis of 40 observational studies published between 2009 and 2024, involving over 1.6 million women.

The authors acknowledged several limitations, including:

• Variations in how different studies classified BMI and gestational weight gain.
• A scarcity of studies from low-income countries that met the inclusion criteria.
• The possibility that unmeasured factors, such as smoking status, maternal age, and ethnicity, could have influenced the results.

Reference

Goldstein RF, Khomami MB, Tay CT, et al. Gestational weight gain and risk of adverse maternal and neonatal outcomes in observational data from 1.6 million women: systematic review and meta-analysis. BMJ. 2025;391:e085710. doi:10.1136/bmj-2025-085710