The journey to pregnancy is different for everyone. Some couples seem to get pregnant by just talking about sex, while others find themselves struggling with infertility for months or even years.
Infertility is a common problem, according to the Centers for Disease Control and Prevention(CDC). Twelve percent of American women ages 15 to 44, regardless of marital status, have trouble getting pregnant or carrying a pregnancy to term.
And while, in most cases, individuals have no control over the factors that contribute to infertility, there are also some modifiable factors that can play a role in getting pregnant. For example, research shows us that being at a healthy weight is beneficial when it comes to conceiving. Of course, it’s important to note that being overweight or underweight is not a reliable form of contraception, and being at a healthy weight does not guarantee fertility—but your weight can impact your baby-making abilities.
First, let’s talk about what we mean by being at a “healthy weight.”
Being at a healthy weight will mean different things to different people, and it depends a lot on your specific health history. Since weight is often associated with certain health markers, health conditions, or even medications, all of those factors may be more important than the actual number on the scale. So speak honestly with your health care provider about your overall health and what a “healthy weight” means for you, as it’s a very individualized measure.
That brings us to BMI (body mass index). Although BMI isn’t a comprehensive tool, it’s going to be referenced a lot here, and that’s simply because a lot of the research we have on fertility uses BMI as a diagnostic tool, even though it has known limitations. Your BMI is an indirect measure of body fat calculated by dividing your weight (in kilograms) by your height (in meters). You can use a BMI calculator like this one, provided by the CDC. It’s an easy, though very limited, screening tool, and it doesn’t take into consideration things like muscle mass, nutrition habits, activity, medical history, or basically anything other than your height and weight. In other words, some healthy people have a high BMI and some people with a normal BMI aren’t as healthy as they think.
Obviously, your BMI can’t tell you everything, so a more thorough assessment could be provided during a physical exam with your doctor. As a side note, when you ask your doctor any questions about weight (or any other issues), you should never feel as though you’re being judged. As doctors, we’re here to help not to judge.
Now let’s dive into how weight affects fertility.
Weight can influence the amount of estrogen in your body.
Most people know that their ovaries produce estrogen, however, a lot of people don’t know that adipose tissue (fat cells) also produces some estrogen. When you’re at a healthy body weight, you have a higher probability of producing an appropriate amount of estrogen, but when you’re overweight or obese, your adipose tissue produces more estrogen than necessary—which can prevent regular ovulation. Without getting too in the weeds, your body requires a fine balance of hormones to ovulate properly, and having too much estrogen can throw off that balance.
On the flip side, when you’re underweight your ovaries make less estrogen, which can also impact ovulation (at ovulation, you need your estrogen levels to rise, helping along the release of the egg from its follicle). According to the Mayo Clinic, “being significantly underweight can affect hormone production and inhibit normal ovulation.” Plus, being underweight can stop menstruation altogether (what’s known as amenorrhea).
Being overweight also increases your risk of insulin resistance.
Not only can insulin resistance lead to type 2 diabetes, but it can also have a negative impact on fertility. Basically, insulin’s job is to move glucose from the bloodstream to the cells. But in cases of insulin resistance, cells “stop listening” to insulin’s request to move glucose into the cells. The body detects that there is lots of glucose in the blood, so, in an effort to help, the pancreas pumps out more and more insulin. And here’s where fertility comes into play: Having a high level of insulin in your blood can cause metabolic disturbances that can affect ovulation.
Insulin resistance, as well as defects in insulin secretion, have been associated with polycystic ovarian syndrome (PCOS), which can also lead to fertility issues. The exact cause of PCOS is unknown, but excess insulin might result in increased androgen production, according to the Mayo Clinic, which can be a problem for ovulation. That said, not everyone with insulin resistance will have PCOS, and women who have insulin resistance without PCOS can also experience ovulatory dysfunction.
Research shows that being at a higher weight can also impact assisted pregnancy rates and pregnancy-related complications.
According to a 2010 review in the Journal of Human Reproductive Sciences, women with a higher BMI don’t respond as well to fertility treatments like in vitro fertilization. A higher BMI also increases the probability of pregnancy-related complications. According to a 2010 meta-analysis published in the journal Human Reproduction, women with a BMI higher than 25 miscarry chromosomally normal fetuses at a higher rate than other women. The exact mechanisms for increased miscarriage rates among obese and overweight women are not currently known, but endocrine problems like PCOS and insulin resistance might play a role.
And according to the American College of Obstetricians and Gynecologists (ACOG), “babies born to obese women [with a BMI of 30 or greater] have an increased risk of having birth defects, such as heart defects and neural tube defects.” The ACOG also warns that obesity increases the risk of pregnancy-related complications like high blood pressure, diabetes, and preterm birth.
Obesity can impact male fertility, too.
If a doctor/friend/family member/anonymous internet commenter says that fertility problems are a woman’s issue, that’s simply not true. According to the CDC, in about 35 percent of couples, a male issue is identified along with a female issue. And in about 8 percent of cases, a specifically-male problem is identified as the sole reason for infertility.
In men, obesity is associated with lower testosterone and impaired sperm quality, as well as a higher rate of erectile dysfunction (ED). A 2007 study of 1,667 men ages 40 and up found that an increase in BMI was associated with a decrease in testosterone. And according to a 2012 study out of Cornell University, men with a waist size of more than 40 inches (the strongest single predictor of developing symptoms of testosterone deficiency) were more likely to have ED.
If you suspect that your weight might be connected to your inability to get pregnant, talk to your doctor.
Struggling to get pregnant can be devastating, lonely, and completely isolating, and finding out that your weight is a factor can add even more confusion and frustration. If losing weight seems like a significant challenge, talk to your doctor to determine what next steps would be most helpful for you. They might suggest a consultation with a registered dietician or offer certain lifestyle changes that can make a difference. According to some research, as little as 5-10 percent weight loss can improve fertility outcomes. So it’s possible that modifications like dietary changes and a healthy exercise regimen could allow you to achieve your goals. And remember, “get fit quick” schemes are just that: schemes. Anything that promises fast weight loss through supplements, cleanses, or too-good-to-be-true workouts is not your best bet, and could even be dangerous.
If you’re underweight or struggling with or recovering from an eating disorder, it’s also beneficial to speak openly with your doctor about these factors. They can connect you to a registered dietitian who specializes in EDs, as well as therapists to help guide you through any complex issues with food and weight.
You should also review your current medications with your health care provider to ensure that they’re safe to take during pregnancy (and not hindering your ability to conceive). Remember to tell your doctor about any over-the-counter medications or supplements, too, not just prescriptions. They can also do a full work-up to determine if something besides your weight is contributing to infertility, as there are many other reasons you might be having trouble. Your doctor can also discuss ways to reduce the stress and anxiety that often comes with infertility, or connect you with a therapist who specializes in all things pregnancy.