We know that having a high BMI hurts live birth rates, both by harming the quality of the eggs and the endometrium. But does that mean you have to lose weight before starting IVF? New research is shedding light on exactly how weight loss impacts an obese person's success with IVF — for better or worse.
"Obesity is definitely a factor that leads to decreased success with IVF," says Mindy Christianson, MD, assistant professor of obstetrics and gynaecology specialising in fertility at Johns Hopkins University of Medicine. Obese people trying to conceive are at an increased risk of miscarriage, and are more likely to have issues with egg quality, Dr. Christianson says. They also might have a decreased response to IVF medications, and certain procedures, such as egg retrieval, can also be more difficult in obese patients, because it's harder to access or visualise the ovaries. Plus, once an obese person becomes pregnant, there's an increased risk of obstetrical issues, such as pre-eclampsia and gestational diabetes, she says.
Given these risks, most fertility clinics have a strict BMI limit for those interested in receiving IVF treatments. "Overall, a BMI less than 30 is preferred, but the pregnancy and live birth rates drop off most with a BMI greater than 35 to 40," she says. People with a BMI higher than 40 can still get IVF, it just involves more preparation. It's offered at her clinic, for example, though patients with a BMI between 40 and 50 are required to have an anaesthesia consultation to make sure they can safely undergo an egg retrieval; anaesthesia itself can be less safe for obese patients.
So, would doctors recommend losing weight to increase your chances of getting pregnant? Dr. Christianson says yes: Patients are encouraged to be at a healthy weight prior to IVF, to improve their outcomes and promote a healthy pregnancy.
"The data that says women who weigh less are more likely to conceive is compelling, almost on the edge of bulletproof," says Jake Anderson-Bialis, co-founder of FertilityIQ, a startup that provides data about fertility clinics and doctors. He says it can be incredibly frustrating for those women with a higher BMI, because they'll hear conflicting advice from credible clinicians, ranging from "don't bother to lose weight" to "you should be prepared to lose the weight."
And that's because the data about IVF and weight also varies. A recent 2017 study in the journal Human Reproduction, found that intensive weight loss doesn't substantially improve live birth rates in obese women scheduled for IVF. According to Dr. Christianson, the women in this study each had a BMI between 30 and 35, so it doesn't provide the full picture. "I would expect more of a difference in outcomes in a morbidly obese group after diet and weight loss, such as those with BMI greater than 40," she says. But another 2013 study found that exercise can actually help obese women's chances of getting pregnant, even if they don't lose weight.
The way that people lose weight can also impact their success with IVF. For example, a 2006 study — confirming everything you already know about crash dieting — found that rapid weight loss doesn't improve IVF success rates, and may even harm them. But for some people, losing weight over a prolonged period of time could layer in additional difficulties. "The challenge is that egg quality also decreases with age, so with an older patient, it may not be feasible to delay fertility treatments too long to attempt weight loss," Dr. Christianson says.
Given all this contradictory information, if you're someone with a BMI between 30 and 35, and your doctor tells you that you need to lose weight in order to get IVF, you have every right to ask questions, Anderson-Bialis says. If a doctor gives you suggestions you're not comfortable with, or turns you away, ask them to explain the data that proves this is the right decision. "If the doctor can’t do that, but makes such concerted recommendations about weight loss, there's probably another host of things the doctor will do," he says. "That's a litmus test of how data-driven they are or whether they rely on their gut, outdated data, and lethargy."
Since it's such a personal process, finding a community of peers who've been through IVF can be a real source of support, Anderson-Bialis says. On the FertilityIQ site, you can search real user reviews about fertility doctors in your area. "Hear from other people how they were treated at that doctor before you decide where to go, and put your trust, hope, and pounds."