How Obesity Affects Your Fertility

Fertility and pregnancy typically involve a complex dance of hormones, biology, timing—and a no small amount of good luck. And with so many factors influencing a person’s ability to get pregnant and deliver a healthy baby, it’s easy to start casting blame when things go wrong. For those with obesity, that pressure can feel exacerbated.

That’s because research has shown that obesity is often linked to infertility. And while many overweight and obese people have no problem conceiving, obesity is the cause of fertility struggles in about 6% of women who have never been pregnant before, according to the American Society for Reproductive Medicine. Obesity can also reduce semen quality, affecting men’s fertility levels.

So if you are interested in starting a family and have obesity, you may be facing increased challenges, notes Christina Boots, M.D., an associate professor of obstetrics and gynecology at Northwestern University Feinberg School of Medicine in Chicago, IL. “There is good data that shows the higher a person’s BMI (body mass index), the lower their success rate at achieving a healthy pregnancy,” says Dr. Boots: Obese women are more likely to have irregular menstrual cycles, a higher rate of miscarriages, and lower success rates of assisted reproductive technologies like IVF. That said, she adds, “BMI is a predictor of health—but it’s an oversimplified predictor. Fertility is far more complicated than just a link.”

Obesity’s Role in Infertility

About 6.7 million women in the U.S. (or about 11% of those in the reproductive-age population) are infertile, according to the Society of Reproductive Surgeons. But it’s not just a female problem: Both women and men can contribute to infertility.

There are several factors that can make it difficult to get pregnant, notes the Centers for Disease Control, including age, smoking, excessive alcohol use, higher physical or emotional stress that results in amenorrhea (missing or absent periods), as well as extreme weight gain or loss and/or being underweight, overweight, or obese. In addition, some cases of infertility are unexplained.

Experts theorize that obesity plays a role in infertility by affecting the body’s sex hormones. In women, fat cells convert a male hormone (androstenedione) into a female hormone (estrone), which in turn affects the complex metabolism that regulates both ovarian and testicular function. “This can negatively impact the menstrual cycle and make ovulation less regular,” explains Caroline Apovian, M.D., co-director of the Center for Weight Management and Wellness at Brigham and Women’s Hospital in Boston, MA, and a professor of medicine at Harvard Medical School.

In men, obesity can create low levels of testosterone and hypogonadism (a failure of the testes to function properly), she adds. Obesity has been linked to a decline in semen quality, along with sexual dysfunction and changes in endocrine functions. High body temperatures, especially around the scrotum (a common occurrence in obesity), can also negatively impact sperm.

In addition, where body fat is stored may play a part in fertility. Research in the Journal of Clinical Endocrinology & Metabolism found women who had more abdominal fat and a higher waist circumference were less likely to ovulate compared to those who had a similar BMI but a lower waist circumference. Obesity may also be linked with other chronic conditions that may have an adverse effect on fertility, such as diabetes.

How Obesity Impacts Fertility Treatments

Obesity may also make it more difficult to achieve a healthy pregnancy with fertility treatments. One study in the Journal of Reproductive Science found that women with a higher BMI and higher level of abdominal fat were less likely to get pregnant with assisted reproductive technology treatments, including hormone-stimulating medications such as clomiphene citrate. In a study in the journal Fertility and Sterility, overweight and obese women who tried gonadotropins (a medication that helps stimulate egg growth) required higher doses and produced fewer follicles at a given dose.

And for those undergoing more invasive (and expensive) IVF treatments, obesity may also tip the odds against a successful pregnancy. Another Fertility and Sterility study found that IVF success rates were significantly less favorable among those with higher BMIs. “It makes things more complicated,” says Dr. Apovian. “With IVF, you are pumping women full of hormones to get as many eggs as possible to fertilize, and if you already have a woman with an abnormal hormone milieu because of obesity, they may have to do more and more cycles—and that is not without complications and huge costs.” Depending on a patient with obesity’s biological clock, her doctor might recommend holding off on IVF until after a she has lost a certain amount of weight. (Some fertility centers also have a BMI cutoff—usually around 45— for undergoing IVF, which is primarily driven by increased anesthesia risk in higher BMI populations.)

Obesity may also impact the health of the pregnancy itself. One meta-analysis found women with obesity were 1.3 times more likely to have a miscarriage; other research in the journal BMC Medicine found that women with obesity who underwent IVF were more likely to suffer an early pregnancy loss. And having obesity can also put you at increased risk of a variety of health problems during pregnancy, including gestational hypertension (high blood pressure), preeclampsia (a serious form of gestational hypertension), and gestational diabetes, along with obstructive sleep apnea, according to the American College of Obstetrics and Gynecology.

Beyond Body Weight

Of all the things that can make it difficult to achieve pregnancy, one of the most important isn’t the number on the scale—it’s the year you were born. “Age plays a huge role in a woman’s fertility,” says Dr. Boots. About one in five (22%) of women age 30 to 39 who are trying to conceive report difficulty, compared to one in eight (13%) of those below age 30, according to the CDC. As women get older, the number and quality of their eggs decline (with more abnormal chromosomes accounting for the latter), so a successful pregnancy becomes less likely. In addition, older women are more likely to have health conditions that can lead to fertility issues. A mother’s age also increases her chance of miscarriage.

Women who have polycystic ovarian syndrome (PCOS), a chronic health condition that affects about one in 10 women of childbearing age, may also have both fertility issues and obesity. With PCOS, in some cases, the ovaries or adrenal glands produce more male hormones than normal, and ovulation is more infrequent, making pregnancy more challenging. (Symptoms of PCOS can include both irregular periods and weight gain.) However, Dr. Boots cautions, BMI is not the only factor affecting fertility in women with PCOS. “Most women with PCOS have some insulin resistance, and that may play a role in ovulation and an ability to conceive apart from BMI,” she notes.

How to Combat Obesity

For couples who are looking to start a family, early action to control obesity is helpful. Although it’s not easy to lose weight through diet and exercise alone, embracing some simple lifestyle changes—reducing processed foods, moving more throughout the day—will help improve overall health and reduce potential complications in pregnancy.

Some research has found that losing 5% to 10% of body weight can increase the chance of becoming pregnant in women who have obesity. Weight loss by itself may improve the chance of unassisted conception, agrees Dr. Boots. However, a 2022 study in PLOS Medicine concluded that women were more likely to conceive by increasing their activity levels without dieting or changing their BMI.

When lifestyle changes alone aren’t enough, you may also want to consider more intensive weight loss measures, such as medications or bariatric surgery. While the latest generation of weight loss medications like Wegovy have shown an average of 15% body weight loss, drugs like this are not without risks, and are considered off-limits for anyone trying to become pregnant, since not enough data is known regarding the safety of these medications and pregnancy. “You need to be off medications at least two months before you conceive,” warns Dr. Boots.

The same goes for bariatric surgery. “If there’s more time, we will try very hard to have the patient consider bariatric surgery; it is the best way to lose significant weight, like 100 pounds, in about a year,” says Dr. Apovian. However, this doesn’t make you prime for pregnancy: Doctors advise putting off trying to start a family until at least one year following bariatric surgery, since having a nutritional deficiency is a common issue in the months following the procedure. “That can be dangerous for both the mother and the fetus,” she adds.

Another strategy if you are concerned about your age and pregnancy is to undergo fertility preservation (egg freezing), then take some time to focus on changes that may help reduce obesity and the odds of success of fertility treatments. Losing weight before you try to start a family may also decrease the risks of pregnancy complications. “It may help to take a year to focus on your lifestyle, whether that’s medications, surgery or something else, and do as much as you can to optimize your health,” says Dr. Apovian.

Perhaps most importantly, if you are navigating both obesity and infertility, be kind to yourself and pay attention to your mental health, says Dr. Boots. “There’s a lot of stigma around infertility in general. People in this situation are already blaming themselves. When you add the issue of weight on top of it all, it becomes an even more delicate situation.”

Talk to your doctor about what is the best approach for you and what other counseling and support is available on your journey to having a baby. And know that you are not alone. Many others with obesity have followed successful paths to pregnancy and more companies are offering fertility treatment benefits for their employees looking to start a family.