Meta-analysis shows benefits of moderate weight loss before IVF

Scientists from Oxford collected 12 randomized trials (N=1,921) and found that weight loss programs before IVF in women with a BMI ≥ 27 increase the overall pregnancy rate, mainly due to spontaneous (non-IVF) conception. The effect on live births and on pregnancies achieved specifically due to IVF was uncertain. That is, some couples who are prescribed IVF become pregnant naturally after losing weight — and do not even proceed to the procedure. The work was published on August 11, 2025 in the Annals of Internal Medicine.

Background of the study

• Why do they even discuss weight before IVF? Excess weight and obesity can interfere with natural ovulation, worsen egg quality and endometrial “readiness,” and increase the risk of pregnancy. Therefore, patients with a BMI ≥27–30 are often advised to lose weight first — but how much this actually improves the chances, especially for a live birth, has long been debated.
• Where was the main gap? There were many small, disparate studies: different diets, different “doses” of activity, sometimes they added medications or very low-calorie programs. The results were mixed: somewhere they saw benefits, somewhere they didn’t. In addition, different studies calculated different outcomes: natural pregnancy, pregnancy after IVF, general pregnancy, live birth. It was difficult to compare “apples with apples”.
• An important practical nuance is timing. For some women, the “gain” from losing weight may come with a “cost of waiting”: fertility declines with age, and taking a break for the sake of losing weight is not always justified. Data is needed to understand where the benefit/risk balance is before starting the protocol.
• Who does this concern first and foremost? Women with ovulation disorders (e.g. PCOS) are more likely to respond to moderate weight loss, sometimes becoming pregnant on their own even before IVF. But it is not clear whether this effect is transferable to everyone and whether it leads to an increase in the success of IVF itself.
• New realities of weight management. Effective medications for weight loss have appeared (GLP-1 agonists, etc.), but they cannot be combined with pregnancy planning; “washout” protocols and safety assessments are required. Therefore, it is especially important to understand what clean lifestyle programs provide and how they affect IVF outcomes.
• Why is meta-analysis of RCTs important? It combines randomized data and helps answer three practical questions:
  1. does losing weight increase the chance of natural pregnancy (before IVF)
  2. does it increase the effectiveness of the IVF protocol as such,
  3. Does the most important thing change - live birth?
• Healthcare context. In many countries, access to IVF is limited by BMI thresholds. Understanding what exactly and how much weight loss helps is important for both clinical decisions and access policy: who should be delayed for weight-related interventions, and who should save time and go to the protocol.

What exactly was analyzed

• 12 RCTs, 1980–2025, participants were women 18+ with BMI ≥ 27, seeking IVF/ICSI.
• Interventions: low-energy diets, physical activity programs + nutrition, in some studies - pharmacotherapy against the background of lifestyle changes.
• Outcomes: natural pregnancy, pregnancy after treatment (IVF), overall pregnancy (both combined), live birth, pregnancy loss. Conclusion: More natural pregnancies, uncertain effect on live birth and on "IVF pregnancies", no signal of increased loss.

Why is that?

Excess weight affects ovulation and hormonal regulation. For some patients, even moderate weight loss (often around several kilograms in studies) can restore spontaneous fertility, and the need for IVF disappears. But if IVF does come to fruition, the increase in success due to the procedure is not yet obvious.

How reliable are the findings?

• The review is a peer-reviewed randomized trial, but many are small and mixed, mixing different weight-loss approaches and patient groups. So the authors and independent experts urge caution in interpreting the results and clarifying which programs work best.
• Nevertheless, the general conclusion is stable: overall, the number of pregnancies is increasing, primarily due to natural conception before IVF.

What does this mean in practice?

• If you have a BMI ≥ 27 and are considering IVF, a structured weight loss program (supervised by a doctor/nutritionist) may increase your chances - perhaps enough to achieve pregnancy without IVF.
• The decision to postpone IVF for the sake of weight loss is an individual one. For some couples, timing is critical (age, ovarian reserve), and the “gain” from losing weight may not outweigh the risks of delay. Discuss your planning horizon with a reproductive specialist. (Experts also remind: GLP-1 drugs are not used during planning/pregnancy - this only concerns the design of future studies.)

What remains unclear (and where to dig next)

• Live birth and 'IVF success': Large trials are needed that separately assess the effects of different interventions (eg, total low-energy diets) on these outcomes.
• Who it helps more: annovulatory forms of infertility (for example, with PCOS) probably benefit more, but there is little data specifically on IVF and live births.
• Equity of access: In some countries, high BMI thresholds limit access to IVF; high-quality, safe weight loss programs could expand access while reducing pregnancy risks.

Conclusion

It is wise to consider medically assisted weight loss before IVF: this can improve the chances – sometimes to the point of pregnancy occurring without the procedure. But it is too early to expect a “magical” increase in the success of IVF itself: here the evidence is uncertain and depends on the type of intervention and the patient’s profile.

Source: Michalopoulou M. et al. The Effect of Weight Loss Before In Vitro Fertilization on Reproductive Outcomes in Women With Obesity: A Systematic Review and Meta-analysis. Annals of Internal Medicine, August 11, 2025. DOI: 10.7326/ANNALS-24-01025.