Weight loss before in vitro fertilization (IVF) could improve reproductive outcomes by increasing the chances of getting pregnant, according to findings published by investigators in Annals of Internal Medicine. The study authors, from the University of Oxford, noted that while chances of getting pregnant were even greater in unassisted conception, the effect on live births remains unclear.1,2
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Obesity and Infertility
As obesity continues to rise globally, researchers have linked the condition to various health complications, including fertility; however, the exact effects of excess weight on reproductive health remain a subject of debate—despite its known risk for other conditions like diabetes, hypertension, and cardiovascular disease.3
Previous studies suggest that obesity negatively impacts reproductive and pregnancy outcomes, but it is unclear if pre-artificial reproductive therapy (ART) weight loss improves results for individuals with both obesity and infertility. Evidence from existing studies highlighted in Nature indicates that obesity in women reduces ovarian response and affects egg and endometrial quality, thereby increasing miscarriage rates during ART. This suggests that while obesity may harm fertility, ART might help mitigate these effects.3
Obesity and IVF
Researchers reviewed 12 randomized controlled trials (RCTs), consisting of a total of 1921 patients from 5 electronic databases between 1980 and May 2025. The women involved in the RCTs were at least 18 years old or older with a body mass index of 27 kg/m² or greater. A BMI of 25 to 29.9 places women as overweight, and a BMI of 30 or higher is obesity.
All women assessed from the RCTs were seeking IVF with or without intracytoplasmic sperm injection treatment for infertility. The study authors noted that 2 independent reviewers conducted screening and data extraction to assess the risk of bias and certainty of evidence. The primary end points of the study were pregnancy and live birth rates—specifically, the number of participants achieving pregnancy without IVF, overall births, and those delivering a live infant. Where applicable, studies were pooled using random-effects meta-analyses.1,2
Among the 12 RCTs, 7 had a high risk of bias. Additionally, the researchers identified that the average participants were in their early thirties with a median baseline BMI of 33.6 kg/m². Weight loss measures that were studied included low-energy diets, an exercise program followed by healthy eating advice, and pharmacotherapy with diet and physical activity advice.1,2
Moderate certainty evidence suggests that pre-IVF weight loss interventions increase total pregnancy rates (risk ratio [RR], 1.21) and unassisted conception pregnancies (RR, 1.47), although their effect on pregnancies from IVF alone is uncertain. Further results demonstrated that these interventions did not appear to be linked with an increase in pregnancy loss rates (RR, 1.05) with moderate certainty, but their impact on live birth rates remains unclear due to very low certainty of evidence (RR, 1.15).1,2
The findings suggest that weight loss before IVF resulted in an increase in total pregnancies, specifically among women with unassisted pregnancy rates. However, larger clinical trials are needed to assess different weight loss interventions since the RCTs in this current study had small sample sizes and a high risk of bias.1,2