Can BMI Affect Fertility?

No two roads to pregnancy and childbirth are alike. Everyone is different, even when it comes to fertility. Some couples are lucky enough to just think about having a child and end up expecting, while others need to undergo months or years of frustration, battling with infertility, before any good news arrives.

Infertility is more common than you think. According to the Centers for Disease Control and Prevention (CDC), about 12 percent of women in America between the ages of 15 and 44 have trouble with either getting pregnant or carrying their baby to full term. Most of the time, individuals have no way to control the factors contributing to their infertility. This could be health-related. Others do have some factors that can be modified to make their chances of pregnancy greater, such as maintaining a healthy weight.

With more Americans becoming overweight or obese, understanding how a healthy weight plays a role in pregnancy is more important than ever.

What Does It Mean To Have a “Healthy Weight”?

First, let’s discuss what it means to be at a “healthy weight,” because this is different for every human being. “Healthy” in and of itself has a unique meaning to everyone, depending on your family and personal medical history. Because your weight is associated with fitness, diet, medications, health conditions, and so on, your weight is a reflection of how healthy you are—but not always.

Some individuals are healthier carrying more weight than their counterpart, even if they are the same height and age. Others might benefit from being leaner.

Now, with that in mind, let’s introduce the body mass index (BMI). The BMI is often used as a standard measure to give you and your healthcare provider a snapshot of your health, but that does not make it infallible. BMI is an indirect measure of body fat based on a ratio between your height (in meters) and weight (kilograms). There are plenty of BMI calculators available on the internet to check your BMI if you are curious.

For now, here are the BMI ranges:

• Underweight: Less than or equal to 18.5
• Healthy: 18.5 – 24.9
• Overweight: 25 – 29.9
• Obese: 30 or greater

However, BMI does not take into consideration your age once you are over 18 years old, nor does it look at lifestyle habits, muscle mass, medical history, or anything else that could factor into your weight. If you are an athlete, for example, you might wind up in the overweight range simply because muscle weighs more than fat. But does that mean you are unhealthy? No.

Likewise, someone who has little to no muscle but is rail thin could end up in the healthy weight range, but they are surely not as healthy as they could be.

So, if you are looking to figure out your ideal healthy weight, it is best to use BMI only as a guideline and discuss your health with a medical professional instead.

How Much Weight Should I Gain When Pregnant?

The safe amount of weight you should gain during pregnancy depends on how much you weigh upon conception. Knowing this will help you understand just how much weight to lose or gain if you are trying to conceive, too.

Here are the BMI ranges and associated pounds you can safely gain:

• Underweight (Less than or equal to 18.5 BMI): Gain between 28-40 pounds
• Healthy (18.5 – 24.9 BMI): Gain between 25-35 pounds
• Overweight (25 – 29.9 BMI): Gain between 15-25 pounds
• Obese (30 or greater BMI): Gain no more than 11-20 pounds

You might be wondering why it is important to gain some weight during pregnancy. Your body is going to be burning a lot of calories supporting you and your child. Without enough body fat, you won’t be able sustain that new life.

Weight & Estrogen Levels

Now, for those of us with female reproductive organs, we are aware that our ovaries produce a hormone called estrogen. We also know that estrogen is responsible for making us fertile. However, most people are unaware that adipose (fat) tissue is also required for the production of estrogen. Women who are at a healthy body weight will produce a normal amount of estrogen, while people who are overweight or obese usually produce far more estrogen than they need.

The human body is all about finding balance, so when you are over-producing or lacking any hormone, complications arise.

Obesity & Fertility

So far, you have learned that being overweight or obese (anywhere between 25-30+ BMI) has a direct effect on how much estrogen you are producing. The other thing that is problematic is the relationship between weight and insulin resistance, which can lead to type 2 diabetes. Insulin can negatively impact your fertility. When you have too much glucose in the body and insulin that is not responding, the pancreas will excrete even more insulin. If it reaches a certain point, your ovulation is impacted.

Both insulin resistance and a lack of insulin have been linked to polycystic ovarian syndrome (PCOS), as well. PCOS plays a role in infertility for many women. While the exact cause of polycystic ovarian syndrome is unknown, it is believed that the excess insulin results in too much androgens, a male hormone, and that stymies ovulation. However, that does not mean that every person with PCOS is going to experience infertility issues.

How Obesity Affects Pregnancy

Studies have found that being at a higher weight will have an influence on assisted pregnancy methods as well as childbirth. A 2010 study published in the Journal of Human Reproduction Sciences stated that overweight or obese women do not respond to in vitro fertilization as well as those at a healthy weight. Moreover, another study found that women with higher BMIs will miscarry more often than those with a healthy BMI.

Moreover, the American College of Obstetricians and Gynecologists (ACOG) found that babies from women with a BMI of 30 or greater have a higher risk of birth defects, such as heart or neural tube defects.


Obesity Affects Male Fertility Too

Now, much of this is making it sound like being overweight or obese solely effects a woman’s fertility, but that is not entirely true. In fact, men are just as likely to suffer from infertility when they fall into the overweight or obese BMI ranges. The Centers for Disease Control and Prevention (CDC) stated that in 35 percent of couples trying to get pregnant, there is a male fertility issues identified alongside the female problem. In 8 percent of infertility cases, the problem is a specifically-male issue that has contributed to the inability to get pregnant.

There is a very simple reason for this. Overweight and obese men oftentimes suffer from impaired sperm quality and lower testosterone levels. Heavier men also experience more erectile dysfunction. One reason for this has been mentioned already: higher body fat levels means higher levels of estrogen.

A study from 2007 looked at 1,667 men ages 40 and up and found a link between higher BMI and a decrease in testosterone levels. Another study from 2012 done by Cornell University reported that men with a waist circumference of 40 inches or more are more likely to have erectile dysfunction.

Underweight & Fertility

Not surprisingly, an underweight woman will also have difficulties with getting pregnant. Underweight is considered a BMI of 18.5 or less. Women who do not have enough body fat will eventually stop making estrogen, which can lead to irregular menstrual cycles and eventually the cessation of ovulation. This most often happens when a woman is dieting too much (restricting food intake too much), exercising too often, or has an eating disorder, such as exercise bulimia or anorexia nervosa.

In order to get pregnant, you have to be ovulating first. Also, your body is going to need enough fat to help support the development of the baby within the womb. Without both, you will find getting pregnant to be a challenge.

If you want to get pregnant but are underweight, talk to your doctor about safe ways to gain weight. Make sure you have been cleared by a medical professional before attempting to get pregnant. Keep in mind that babies who are born from underweight mothers are often at risk of preterm or premature birth and often have very low birth weights, which can lead to growth and health problems later.

What To Do About Your Weight & Fertility

Infertility can be devastating news for both parties, especially when you do not have a clear answer about why this is happening to you. You might feel devastated, confused, or even disillusioned about your body. If you suspect that your weight is to blame—whether you are underweight or overweight—you should schedule an appointment with your doctor.

Losing weight (and gaining weight) will certainly be a challenge, but if you truly want to get pregnant and deliver a healthy baby safely, then it is time to figure out how to go about it. You can also schedule a meeting with a registered dietitian or nutritionist to help you figure out what you should be eating and how much. Sometimes a change in your diet is all you need to drop a few pounds.

Research has found that even losing just 5-10 pounds can improve your chances of getting pregnant.

However, you should avoid falling for the empty promises of fad diets or exercises programs that promise to help you lose the weight fast. There are no schemes for losing weight quickly that are healthy. Adopt the mindset that this is a lifestyle change that will not only help you grow your family but will promote a longer life with more independence in the later years. Avoid any cleanses, supplements, or items that make promises that sound too good to be true. Most of time, it is a waste of time and money.


If you happen to be underweight or are struggling with an eating disorder, the first step is to acknowledge that you indeed have a weight problem. You may have to first overcome the challenges that are keeping you from eating. The best person to speak with in that case is a cognitive-behavioral therapist, since they can help you find the root cause of your eating disorder and absolve the psychological traumas that have resulted in the eating disorder.

Lastly, if you are on medications and trying to get pregnant, consider what you are taking. Some drugs are not safe to take during pregnancy and may also affect your ability to conceive. Discuss with your doctor about any alternatives that are available and disclose any information about over-the-counter medications or supplements that you are taking. You can also discuss how stress could be affecting your fertility. Do not forget to mention any medical problems in your family history that could be influencing your fertility.

Wrapping It Up

Your BMI can definitely affect your fertility. Women who are overweight or underweight will both struggle to get pregnant because of hormonal imbalances and other health issues. Overweight or obese men can also be impacted by infertility. Additionally, people with higher BMIs also struggle to get pregnant even with assisted pregnancy methods. Therefore, if you are trying to get pregnant, it is important to think about your health and weight and how healthy you truly are.

Fortunately, you can lose or gain weight with a little effort. Soon, you will receive wonderful news, so don’t give up.

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