Women with obesity who participate in weight loss programmes before the beginning of in vitro fertilisation (IVF) are almost 50 per cent more likely to conceive naturally than those given little or no weight loss support, a major review of evidence has found.
Analysis of 12 international trials involving nearly 2,000 women revealed weight-loss interventions not only helped women with obesity conceive, but also increased the odds of any pregnancy, natural or through IVF by 21 per cent.
The findings, published in the Annals of Internal Medicine, come as the NHS restricts access to funded IVF for women with a Body Mass Index (BMI) over 30. Researchers say providing structured weight loss programmes could not only enable more women to be eligible for NHS-funded IVF but may also significantly increase their chances of conceiving naturally.
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Led by the University of Oxford, the review analysed 12 randomised controlled trials (RCTs) of women with obesity who were offered a weight-loss intervention before planned IVF, across five electronic databases up until May 2025. Researchers identified seven of the RCTs as having a high risk of bias due to poor study design, which may affect the reliability of the data in these studies.
The interventions ranged from diet and exercise programmes to weight loss medications such as orlistat and older GLP-1 agonists, earlier versions of the drug class that now include Ozempic and Wegovy.
Women lost an average of 4kg more
Women in the intervention groups lost an average of 4kg more than those in the comparison groups. The review shows pre-IVF weight-loss programmes were linked to higher overall pregnancy rates, including a 47 per cent increase in natural conception. There was no clear evidence that weight-loss interventions improved pregnancy rates from IVF alone and they had no impact on miscarriage rates.
Dr Moscho Michalopoulou, lead author from Oxford’s Nuffield Department of Primary Care Health Sciences, said the findings offer hope to women with obesity who currently face the double challenge of higher rates of infertility and potential exclusion from NHS-funded IVF.
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He explained: ‘Our findings suggest that offering structured weight loss support could improve the chance of conceiving naturally, which may avoid the need for IVF treatment. Programmes that help women achieve greater weight losses have the potential to help more women achieve a successful outcome, and should be tested in larger high-quality trials.’
Improving equity of access to fertility treatment
While the review provides the best evidence to date of the benefits of weight loss for conception, the researchers emphasise that the small sample size and bias in some studies highlight the need for more extensive trials to confirm the results, particularly the effect on live births. This effect remains unclear but the pooled data suggest weight loss interventions could increase live birth rates by 15 per cent. When the researchers restricted the analysis to low-energy diet replacement programmes, which led to greater weight loss, this correlated with an increase in live births.
Dr Michalopoulou added: ‘We need efficient, evidence-based pathways that give them the best chance of success. Our work suggests that for many women with obesity, an intensive supported weight loss programme could help them to conceive naturally or make it possible to access IVF services.’
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Associate Professor Nerys Astbury, from the University of Oxford, noted: ‘This isn’t just about improving pregnancy rates – it’s about improving equity of access to fertility treatment. We know that people from more deprived areas and those from certain ethnic backgrounds are more likely to live with obesity. Policymakers should consider whether integrating structured weight loss support into fertility services could improve outcomes for patients, while potentially reducing overall costs by increasing the number of women who conceive naturally.’