The Effect of Weight Loss Before In Vitro Fertilization on Reproductive Outcomes in Women With Obesity : A Systematic Review and Meta-analysis

Abstract

Background: It is unclear whether weight loss before in vitro fertilization (IVF) improves reproductive outcomes in women with obesity.

Purpose: To assess whether weight loss interventions before IVF improve reproductive outcomes.

Data sources: Five electronic databases through 27 May 2025.

Study selection: Randomized controlled trials (RCTs) in women with obesity who were offered a weight loss intervention before planned IVF.

Data extraction: Dual independent screening, data extraction, and assessment of risk of bias (RoB) and certainty of evidence. Primary outcomes were pregnancy and live birth rates. Where appropriate, studies were pooled using random-effects meta-analyses.

Data synthesis: Twelve RCTs (1921 randomly assigned participants) were included, 7 of which had high RoB. There was moderate certainty that pre-IVF weight loss interventions were associated with an increase in total pregnancy rates (risk ratio [RR], 1.21 [95% CI, 1.02 to 1.44]; 11 studies) and pregnancies resulting from unassisted conception (RR, 1.47 [CI, 1.26 to 1.73]; 10 studies), whereas the effect on pregnancies resulting solely from IVF was uncertain. Weight loss interventions were not associated with pregnancy loss rates (RR, 1.05 [CI, 0.98 to 1.13]; 8 studies; moderate certainty), but their effect on live birth rates was unclear (RR, 1.15 [CI, 0.95 to 1.40]; 9 studies; very low certainty).

Limitations: Studies were small, had high RoB, and often did not report important outcomes, such as live births. Substantial clinical and methodological heterogeneity was unexplained by exploratory analyses.

Conclusion: Weight loss interventions before IVF appear to increase the chances of pregnancy, especially unassisted conceptions. However, studies were small, and heterogeneity made it difficult to determine the benefit of any particular intervention.

Primary funding source: National Institute for Health and Care Research Applied Research Collaboration Oxford and Thames Valley. (PROSPERO: CRD42023441457).

Figure 1. Effect of weight loss interventions on: (A) unassisted pregnancy, (B) treatment-induced pregnancy, and (C) live birth rates, grouped by intervention and comparator type, sorted by mean difference in weight change between groups

n: number of events; N: number of participants randomized; CI: confidence interval; BMI: body mass index; PCOS: polycystic ovary syndrome; CI: confidence interval; DL: DerSimonian–Laird; HKSJ: Hartung–Knapp–Sidik–Jonkman; MH: Mantel-Haenszel. All but one (Becker 2015) diet interventions were accompanied by physical ativity advice; In Kiel 2018, the main intervention being tested was a physical activity program, but it was also accompanied by some dietary advice; All but one (Einarsson 2017) low-energy diet interventions were accompanied by some physical activity advice; All pharmacotherapy interventions were accompanied by both diet and physical activity advice. Mean age for women specifically seeking IVF was unknown from Mutsaerts 2016; % PCOS in the sample was unknown from Mutsaerts 2016, Wang 2021 and Kiel 2018, either because it was not reported, or it was not reported specifically for women seeking IVF; Espinos 2017 did not provide weight data at follow-up for the comparator, therefore it was not possible to calculate the mean difference in weight change between groups; Li 2022 reported events and weight data from per protocol analysis only; Price 2020, 2021 reported weight data from per protocol analysis only; We were able to obtain weight and total conception data for women specifically seeking IVF from authors of Mutsaerts 2016. A. Becker 2015 only reported unassisted pregnancy rates, therefore, total pregnancy rates are not known; C. Unassisted pregnancies seem to have been taken into account in live birth rates reported by Einarsson 2017, Sim 2014, Price 2020, 2021, Espinos 2017, Wang 2023, and Wang 2021; For Moran 2011 and Li 2022, it is suggestive that unassisted pregnancies were not taken into account in the reported live birth rates.