Weight Loss Before IVF Boosts Pregnancy Rates, Especially Unassisted Conception, Study Finds
A new systematic review and meta-analysis published August 12 in the Annals of Internal Medicine suggests that weight loss prior to in vitro fertilization (IVF) is associated with increased pregnancy rates, particularly through natural conception, potentially reducing the need for medical intervention.
Obesity and Fertility: A Complex Relationship
Obesity is increasingly recognized as a significant factor impacting reproductive health. According to a 2021 opinion from the American Society for Reproductive Medicine, obesity can lead to ovulatory dysfunction, reduced responsiveness to ovulation-inducing agents, impaired oocyte and endometrial function, and lower birth rates following IVF. Previously, the impact of weight loss on reproductive outcomes for women undergoing IVF remained largely unknown.
New Research Reveals Positive Correlation
To address this gap in knowledge, researchers led by Moscho Michalopoulou, MSc, DPhil, of Oxford University in the United Kingdom, analyzed data from 12 randomized controlled studies (RCTs) encompassing 1,921 women with obesity who were preparing for IVF. The participants, primarily from upper-middle and high-income countries, had a median body mass index (BMI) of 33.6 kg/m². Most were in their early 30s, and weight loss across the studies tended to be moderate. Approximately 25% of women across nine of the studies had polycystic ovary syndrome (PCOS).
The studies varied in their weight loss interventions, with active phases lasting between 5 and 24 weeks, with a median duration of 12 weeks. Control groups received either standard care, or in six of the studies, no or minimal intervention. Participants in the intervention groups lost an average of 4 kg more than those in the control groups. The researchers found that the difference in weight loss was most pronounced when comparing interventions to groups receiving no or minimal support. Follow-up periods for reproductive outcomes ranged from 1.3 to 18 months for intervention groups and 4.3 to 24 months for controls.
Unassisted Pregnancy Rates Show Significant Improvement
Analysis of ten studies, including 1,466 participants, revealed a statistically significant association between weight loss interventions and increased unassisted pregnancy rates (relative risk, 1.47; 95% CI, 1.26 – 1.73). However, the authors caution that many studies reported limited numbers of unassisted pregnancies, resulting in wide confidence intervals. Interestingly, weight loss appeared to be less effective in improving unassisted conception rates among women with PCOS.
“The findings suggest that weight loss can improve a woman’s chances of conceiving naturally before needing to undergo IVF,” one analyst noted.
Uncertainties Remain Regarding IVF Success and Live Births
While the study demonstrated a positive impact on unassisted pregnancies, the evidence regarding the effect of weight loss on pregnancies achieved through IVF was inconclusive. Furthermore, data on live births were limited and heterogeneous, making it difficult to draw definitive conclusions about the long-term impact of weight loss interventions. The investigators acknowledged that a lack of comprehensive follow-up on pregnancy outcomes was a key limitation of their analysis.
Need for Further Research
The study authors emphasized the variability in study design and participant characteristics as another weakness, potentially influencing the results. Alan S. Penzias, MD, writing in an accompanying editorial, echoed this sentiment, highlighting the need for future studies to include comprehensive data on both pregnancy loss and live birth rates for both medically assisted and unassisted pregnancies.
Penzias, who directs the Fellowship Program in Reproductive Endocrinology and Infertility at Boston IVF/Beth Israel Deaconess Medical Center, underscored the importance of a woman’s age in fertility, stating, “A woman’s age is the strongest predictor of successfully becoming pregnant.” He cautioned that the time required to achieve weight loss must be carefully balanced against the potential benefits of weight loss on natural conception and the age-related decline in fertility. He also noted that a woman’s desired family size, a factor unaffected by weight loss, should also be considered when deciding whether to pursue IVF.
Cate Varney, DO, an associate professor at the University of Virginia School of Medicine, emphasized the established link between obesity and infertility, stating, “There is a gap in the data between the association and modifiable risk.” She added that determining the optimal timing and amount of weight loss is crucial to navigating the trade-offs between delaying IVF and the impact of age on fertility.
This research was supported by the National Institute for Health and Care Research Applied Research Collaboration Oxford and Thames Valley. The study authors and editorialist Penzias reported no relevant financial relationships. Varney is an advisor and in the speaker’s bureau for Eli Lilly.
