Weight and Infertility
If you are struggling with infertility or considering IVF, and you also happen to live in a larger body, chances are your RE (reproductive endocrinologist, aka fertility doctor) has recommended you lose weight. Some clinics may even limit access to IVF treatment to women below a certain BMI.
Often, REs don’t specify why weight loss is necessary to proceed with IVF. Sometimes, they’ll mention statistics suggesting that weight loss can lead to a higher live birth percentage (the goal in IVF). But what does the research say about weight and IVF? Do these weight loss recommendations come with sufficient data to support them?
In 2015, the American Society for Reproductive Medicine issued a committee opinion on obesity* and fertility. The report details the correlation between weight and several factors critical to fertility (e.g., ovulatory dysfunction, egg quality, endometrial function, maternal-fetal environment) and goes on to recommend pre-conception weight loss via “lifestyle modification,” medical treatment, medications (including stimulants), or weight-loss surgery, while noting that it is “unclear” whether conception following weight-loss surgery can result in preterm birth, miscarriage, neonatal death, or malformation. The report focuses on the importance of being in a lower-weight body in order to conceive and birth successfully though states that “To date, however, there is no strong evidence to suggest that preconception weight loss in women improves IVF-related pregnancy outcomes.”
While it could be that thinner women have a higher success rate than fat women with fertility procedures, taking fat women and trying to make them thin in order to achieve better outcomes doesn’t seem to work.
What Does the Research Say Regarding Weight and IVF?
In a landmark 2016 study, 577 obese* women were randomly assigned to a lifestyle intervention (i.e., weight loss) group or proceeded directly to fertility treatments. Contrary to what you might expect given most medical recommendations, pre-IVF weight loss did not improve treatment outcomes; in fact, those in the lifestyle intervention actually experienced a lower IVF success rate than their non weight-loss counterparts.
In another randomized control trial, in 2017, 317 women with a BMI between 30-35 were also divided into weight loss (via a low-calorie liquid diet) and control groups prior to undergoing IVF. The weight loss group had a marginally higher live birth rate, though the difference between the two groups was not statistically significant.
Overall, these data on weight and IVF suggest that weight loss does not significantly improve live birth rates. The relationship between weight and IVF isn’t as clear as we’d assume, given what most doctors advise. While being at a lower initial weight might help with IVF outcomes, intentional weight loss takes a toll on the body. It’s possible that significant food restriction and/or overexercise don’t allow for ideal fertility outcomes.
It makes sense. A starving, stressed body isn’t a fertile body.
In addition, intentional weight loss often results in longer term weight gain, weight cycling, and disordered eating. As was observed in the 2016 study above, weight loss is challenging and many women won’t meet their weight loss targets or will drop out during the process.
While it might be that higher weight bodies are more prone to certain issues that negatively impact conception and live birth rates (e.g., anovulation, miscarriage), there is no good evidence to support that losing weight prior to starting IVF mitigates these issues. In fact, intentional weight loss may create additional physical and psychological challenges. It is recommended that REs and IVF clinics consider this research when making weight-related recommendations to their patients.
*the words obesity/obese are taken from the original studies.