Weight loss interventions for people who are overweight and obese undertaken before turning to IVF could increase the chances of getting pregnant naturally.
This is the conclusion of researchers from University of Oxford who reviewed 12 past studies involving nearly 2,000 patients from 1980 to May of this year.
They compared a woman’s weight to how likely they were to become pregnant either without IVF (unassisted pregnancy), with IVF (treatment-induced pregnancy) and overall (unassisted plus treatment-induced)—as well as whether they delivered a live baby.
“All participants in the included studies were candidates for IVF. Before having IVF, they were offered weight loss support. The women who got pregnant naturally, ended up not needing to have IVF,” study author and dietician Moscho Michalopoulou told Newsweek.
Inclusion criteria included studies conducted on women who were at least 18 years old with a BMI of 27 kg/m² or greater who were seeking IVF with or without intracytoplasmic sperm injection treatment (ICSI) for infertility.
“IVF and ICSI are assisted reproductive techniques where oocytes [cells involved in reproduction] are fertilized outside the body, before embryos are transferred back into the woman’s womb. The key difference is how the fertilization is achieved,” Michalopoulou explained.
“Regular IVF egg and sperm are typically mixed in a Petri dish, with ICSI, the sperm is directly injected into the egg.”
The researchers found that participants were typically women in their early 30s with a median baseline BMI of 33.6 kg/m².
The weight loss interventions studied included low-energy diets, an exercise program accompanied by healthy eating advice and pharmacotherapy accompanied by diet and physical activity advice.
“Low-energy diets, also known as total diet replacements, typically use liquid formula products to replace real food and induce a much larger energy deficit with total energy intake of no more than 1000 kcal/day, followed by gradual reintroduction of foods for weight stabilization,” Michalopoulou explained.
She said these are safe for women when supervised and supported to follow such a program, with a lot of literature on the effectiveness of these diets.
“In this one study, the main intervention being tested was high-intensity interval training (referenced as Kiel 2018 in the paper). At the same time, participants were advised to eat healthy as per national healthy eating recommendations,” said Michalopoulou.
In terms of the ‘pharmacotherapy’ intervention, she added, “Participants were instructed to take weight loss medication which was the main intervention being tested, but at the same time, they were given healthy eating advice or a hypocaloric diet [low in calories], plus advice on how to increase their physical activity, e.g. doing more steps, or doing exercise.”
Overall, weight loss interventions before IVF were associated with greater unassisted pregnancy rates, according to the researchers.
“Regardless of weight loss method used, across all studies, women with obesity who participated in a supported weight loss program before IVF had 47 percent higher chances of getting pregnant naturally, compared to women in the comparator groups who typically received standard care,” said Michalopoulou.
“Therefore, more women in the intervention than in the comparator groups did not need to have IVF treatment to get pregnant, as they got pregnant naturally.”
However, evidence was inconclusive on the effect of weight loss interventions on treatment-induced pregnancies.
“It is unclear if weight loss interventions before IVF have an effect on the chances of getting pregnant through IVF. In some studies there were more IVF pregnancies in the intervention groups compared to standard care, in some others there were fewer IVF pregnancies compared to standard care—and in some others there was no difference in IVF pregnancy rates compared to standard care,” Michalopoulou explained.
“This large variability, combined with other methodological issues of the included studies, prevent us from having a clear conclusion on whether weight loss programs before IVF have an effect on IVF-induced pregnancy success or not.”
Evidence on the association between weight loss interventions before IVF and live births was uncertain—mainly because there were fewer studies that reported live birth outcomes—although there was moderate certainty of no association with pregnancy loss.
“Obesity can lead to female infertility through hormone imbalance, insulin resistance, inflammation, and polycystic ovary syndrome. All of these can lead to ovulatory dysfunction,” said Michalopoulou.
“Obesity has also been associated with lower IVF success for women with infertility, such as requiring higher doses of treatment, reduced response to the medications, reduced chances of getting pregnant, and increased chances of miscarriage if a pregnancy is achieved.”
“Maintaining a healthier weight can help improve hormone balance, increase insulin sensitivity, reduce inflammation, and improve ovulation. For women seeking IVF, lowering their BMI to healthier levels may improve sensitivity and response to the treatment, improve egg quality and uterine function, and as a result, increase their chances of getting pregnant.”
However, everyone is different, the researcher noted. “Many larger women will have healthy pregnancies. But evidence shows that starting pregnancy carrying too much weight and gaining too much weight during pregnancy are both associated with greater risks of complications. This does not mean that every woman living with obesity will develop these complications—just that there will likely be more complications than in women who start pregnancy in the normal BMI range”
The researchers hope their systematic review and analysis of randomized controlled trials will lead to more advanced trials.
“We already know weight loss can help with fertility, but whether it improves IVF outcomes is far less certain. This review sheds some light, but most of the studies are small and at high risk of bias, so the results need cautious interpretation. IVF bypasses many obesity-related barriers, but what is still unclear is if delaying treatment for weight loss truly boosts success rates,” said Ying Cheong—a professor of reproductive medicine of the University of Southampton who was not involved in the present study—in a statement.
“Weight loss interventions before IVF appear to increase the chances of pregnancy, especially through natural conception, which may negate the need for IVF treatment, and does not seem to increase the risk of pregnancy loss. This offers hope to women with obesity and infertility,” Michalopoulou said.
“However, the evidence is limited and unclear on whether weight loss interventions before IVF have an effect on live birth rates, and more evidence from larger, high-quality trials is needed to test this.”
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Reference
Michalopoulou, M., Jebb, S. A., Hobson, A., Khaw, S. C., Stevens, R., Melo, P., Haffner, S. J. P., Clay, K. S., Mounsey, S., Granne, I., Lim, L., Child, T., & Astbury, N. M. (2025). 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, 178(9). https://doi.org/10.7326/ANNALS-24-01025
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