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What is the Relationship Between Obesity and Fertility

What is the relationship between obesity and fertility? 

Obesity is defined as a body mass index (BMI) above 30. Because obesity is so common (more than 40% of Americans have obesity), 25% of women in the US who become pregnant have obesity. A lot of research has shown that obesity adversely impacts a woman’s chance of becoming pregnant: rates of natural pregnancy are lower as BMI gets higher. It is also true that a woman with excess weight before pregnancy is at a greater risk of many complications during a pregnancy that can affect her own health (such as high blood pressure and gestational diabetes) and that of the baby (such as birth weight). 

What is it about body fat that affects fertility?

The biology that underlies the relationship between body fat and the ability to become pregnant is fascinating–but complicated. Adipose tissue (fat, as we know it) is very important for hormone regulation. Adipose cells convert male hormones to female hormones, so having excess fat tissue can disrupt the fine balance between male and female hormone levels. And this in turn can disrupt the elegant cycles that result in the reproductive system releasing eggs (ovulation).  So women who have higher BMI have lower rates of ovulation. However, this is not the full story, because even when they have normal ovulation, women with obesity have lower pregnancy rates.

Interestingly, obesity affects male fertility as well. Men with obesity are more likely to have low sperm count and motility (ability to swim). Men who have excess weight can have increased body temperatures and higher female hormone levels, both of which impair fertility.

Does weight loss improve fertility? 


Research has shown that if a woman with obesity can lose weight, she is more likely to get pregnant. In fact, losing just 10% of starting weight helps regulate the menstrual cycle, and increase rates of ovulation and spontaneous pregnancy. Pregnancies that start at a lower weight also have lower rates of complications for the mother and the baby.

What about weight loss for women who need assisted reproductive technology such as IVF?

What we know about how weight loss impacts success rates for women who need assisted reproductive technology such as in vitro fertilization (IVF) comes from two large randomized controlled trials which studied diet, exercise, and weight-loss interventions in women with obesity interested in pregnancy. Women who lost weight before undergoing IVF had an increased likelihood of becoming pregnant spontaneously. Women who lost weight and still needed IVF did not have higher rates of live births, but during their pregnancies had a lower risk of high blood pressure, pre-term birth, and metabolic syndrome/insulin resistance.

And beyond the research, a very important consideration for women who have obesity as well as infertility is that in most centers across the US, a BMI below 35 is required to undergo IVF. This has to do with the increased risk that higher BMI confers during anesthesia. So for women with a BMI above 35, achieving weight loss can mean the difference between being offered the treatment, or being ineligible for it. 

Can women with infertility and obesity be successful at weight loss? 

Absolutely. Weight loss is possible even for women who have struggled with their weight for a long time, and who are also going through fertility treatments that can affect their weight.

Many people are not aware of a subspecialty of medicine called obesity medicine, which focuses on helping individuals lose weight to improve their health. Obesity medicine specialists work to understand the many factors that contribute to a person’s weight and to evaluate the many ways in which weight is affecting the person’s health. Then they use a wide range of science-backed methods to help each individual find their unique path to successful weight loss. Weight management is usually a team effort and works best when it also leverages the experience of other health care professionals, such as dietitians.

At Form Health, we pair each patient with a board certified physician and a weight management dietitian. We work with patients on incremental changes that add up to a healthy mindset and a healthy lifestyle. The goal is establishing habits that can be continued during pregnancy and beyond – because avoiding excess weight gain during pregnancy is key, since (unfortunately) postpartum weight retention is a fact of life. All of our care is delivered through a phone ‘app’ to make it as convenient as possible to get the kind of support that we know successful weight loss requires. Our team works closely with the fertility specialist towards the mutual goal of helping our patients have healthy pregnancies and healthy babies.

So although it can be challenging to discuss obesity and fertility, there are positive steps anyone can take towards getting healthier as part of planning for pregnancy. Women who want to become pregnant are uniquely motivated to achieve their health goals, and with the right medical expertise and support from a compassionate team, weight loss is possible

Form Health is excited to work with VCRM patients in helping them on their journey

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