Two thirds of women gain too much or too little weight in pregnancy: Global study

Key points

• Higher and lower than recommended gestational weight gain is associated with increased pregnancy complications
• Support is needed to improve health for women across the globe
• Findings may help inform global standards for healthy weight gain in pregnancy

Around two-thirds of pregnancies have weight gain that is more or less than recommended and is associated with complications such as preterm birth, large birth weight, and admission to intensive care.

The findings are part of a Monash University-led systematic review of data from 1.6 million women, published by The BMJ.

Gaining too much or too little weight during pregnancy, known as gestational weight gain or GWG, represents combined growth of mother and baby, and is associated with increased risks to both mother and child.

Each year 130 million births occur globally in total, in the context of increasingly unhealthy and processed food supply and environmental drivers, causing an epidemic of excess GWG.

First author Dr Rebecca Goldstein, from the Monash Centre for Health Research and Implementation (MCHRI), said the study’s results underlined the need for international action.

“These findings reinforce the need for international reference standards for healthy GWG alongside lifestyle support and public health measures to improve outcomes for mothers and babies worldwide,” Dr Goldstein said.

Most countries rely on Institute of Medicine GWG guidelines*, but these are based on data from predominantly Caucasian women in high income countries in the 1980s, so they don’t reflect ethnically diverse populations across low, middle and high-income settings, or changes in food supply and environment that are driving global trends such as rising weight (BMI).

In response, the World Health Organization (WHO) has launched an initiative to develop global healthy GWG standards aimed at defining optimal GWG recommendations across diverse settings.

To support this initiative, Monash University researchers and collaborators from the WHO analysed data from 40 observational studies involving 1.6 million women aged 18 and over from five of the six WHO defined world regions that reported pregnancy outcomes according to BMI and GWG from 2009 to 2024. Of these 40 studies, 36 were considered to be high quality.

Around half (53 per cent) of study participants had a healthy pre-pregnancy BMI, with others classified as below (6 per cent), above (19 per cent), or well above healthy weight (obese) (22 per cent). Only a third (32 per cent) had GWG within recommended ranges, with 23 per cent gaining below and 45 per cent gaining above recommended.

Based on WHO BMI criteria, the research study found that GWG below the recommended range was associated with: lower risk of caesarean delivery; a large for gestational age infant; and high birth weight (macrosomia) but higher risk of preterm birth; a small for gestational age infant; low birth weight; and respiratory distress.

Conversely, GWG above the recommended range was associated with: a higher birth weight and a higher risk of caesarean delivery; hypertensive disorders of pregnancy; a large for gestational age infant (macrosomia), and admission to a neonatal intensive care unit; and a lower risk of preterm birth and a small for gestational age infant.

Similar patterns were apparent when Asian BMI categories were used in studies conducted in this world region.

The researchers point to some limitations, such as variations in BMI and GWG classifications, and note that few studies from low income countries met their inclusion criteria, limiting diversity. Nor can they rule out the possibility that other unmeasured factors, such as smoking status, age and ethnicity, may have influenced their results.

However, Senior author Professor Helena Teede, who is Director of the Monash Centre for Health Research and Implementation, and an Endocrinologist at Monash Health, said the study supported the need for a global approach.

“Our findings inform and support the need for optimised, evidence-based WHO international GWG reference standards based on individual patient data, applicable to contemporary and diverse global populations,” Professor Teede said. “This work builds on and improves current recommendations and highlights the need for multi-level support to improve the health of mothers and babies worldwide.

“Whilst this work supports guidance on healthy GWG, it will need to be incorporated into individualised care to meet the needs of those in pregnancy, limiting stigma and optimising healthy outcomes for women and the next generation. Ultimately, the burden of health impacts shown here mandate action to support women across policy, healthcare and individual level solutions for the health of mothers and babies.”

Read the research paper in The BMJ: Gestational weight gain and risk of adverse maternal and neonatal outcomes in observational data from 1.6 million women: systematic review and meta-analysis
DOI: 10.1136/bmj-2025-085710

This study involved researchers from Monash University, Monash Health, the World Health Organization’s Department of Nutrition and Food Safety, the National Institute of Perinatology in Mexico, Universidade Federal do Rio de Janeiro (UFRJ) in Brazil and California Polytechnic State University.

Background*

In 1990 the USA’s Institute of Medicine (IOM), now known as the National Academy of Medicine  generated gestational weight gain guidelines based on a modest sized population of predominantly white women from 1980 in the US, with a mean body mass index (BMI) of 24 and age of 26 years, focusing on the outcome of low birth weight. The 2009 IOM guideline update incorporated WHO BMI categories and broader outcomes, varying recommended GWG by maternal BMI. These guidelines have since provided an important international reference point. However, the evidence underpinning them reflects the population and priorities of that era, characterised by lower maternal age and BMI, with limited ethnic diversity and a narrow high income setting.