Weight and fertility

Disclaimer: This article has been sponsored by Novo Nordisk

Top things to know:

• Fertility is complicated and influenced by many different factors, including age, body weight, medical conditions, and lifestyle

• Both people who are underweight and overweight can have difficulty becoming pregnant

• Simple, consistent lifestyle changes can improve the chances of conceiving

• Clue Conceive can help you identify your most fertile days and support your path to pregnancy

How weight and fertility are linked

Trying to conceive (TTC) can bring up many different feelings, and the process comes with a lot of unknowns. Several factors may impact fertility, including age, body weight, medication or substance use, and medical conditions (1). 

While women often carry the burden for fertility concerns, male factors also play a key role. Despite this, many women feel alone while navigating a fertility journey.

Body weight is one of the factors that can impact fertility (1). A healthy body weight for reproductive health varies from person to person. 

Maintaining a healthy body mass index (BMI) is associated with the best outcomes while trying to conceive (2). However, BMI is not a perfect system. Our body weights are influenced by our genetics, environment, and personal experiences (3). 

In this article, we will break down the impact of body weight on fertility outcomes and the small changes you can make to ensure you are your healthiest and strongest self before pregnancy.

Both low and high body weight can impact the ability to become pregnant. When people talk about healthy body weight for fertility, they are usually referring to BMI. BMI is a measure of weight related to height. It does not account for body composition (amount of body fat, muscle, or bone) (4).  

BMI is often criticized as an imperfect tool. It was developed from research on men and does not take body fat percentage or fat distribution into account (5). 

However, research shows that where fat is located on the body matters. Central belly fat carries a higher risk for metabolic and heart diseases than fat on the hips and thighs (6). This is especially important when talking about women, whose higher estrogen levels often lead to more body fat storage in the hips and thighs (7). 

Despite its limitations, BMI is still the main measurement used in research on body weight and fertility.

BMI categories include (8):

BMI outside the healthy weight category can negatively affect egg quality and interfere with ovulation (the release of the egg from the ovary into the fallopian tube). This may lead to difficulties in becoming pregnant (9).

Higher weight and trying to conceive

People in larger bodies frequently get pregnant without difficulty. However, higher BMI is linked to hormonal changes in the body that can affect fertility. 

People with higher body fat levels have more adipose (fat) tissue, and this changes the hormone balance in the body. They may also have higher leptin, insulin, and cholesterol levels (9). Adipose tissue increases levels of hormones such as estrogen and androgens (including testosterone) (9). Inflammation levels also tend to be higher (9). 

This different balance of hormones can also interfere with ovulation (9). It can also negatively affect egg quality and maturity (9). Some researchers even think that the increased inflammation seen in obesity can affect how an embryo implants in the uterus (9). Together, these factors may make it more difficult to conceive.

Women who are overweight or have obesity may take longer to become pregnant, and some studies suggest a higher likelihood of infertility (10). They may also respond differently to fertility treatments, such as ovarian stimulation or egg retrieval (11). 

Pregnancy risks and complications

Having a higher BMI is linked to increased risks during pregnancy. This can include a higher risk of miscarriage, including recurrent (repeated) miscarriage (12). It is also linked to an increased risk of complications, such as gestational diabetes, high blood pressure, and cesarean birth (12).

Not everyone with a higher BMI will have these outcomes. It’s important to talk to your healthcare provider about your unique health history. Other factors, such as being over 35 or having conditions like polyendocrine ovarian metabolic syndrome (PMOS, previously known as PCOS), may also influence fertility (13).

PMOS and fertility

PMOS is a complex hormone condition. It isn't exactly clear what causes it, but it’s likely a combination of genetic, lifestyle, and environmental factors (14). 

People with PMOS often have high levels of androgens (like testosterone). This hormone imbalance can prevent ovulation, and it can also cause irregular menstrual cycles. Some people may skip periods or experience heavy or frequent bleeding. They may also have acne or excess hair growth on the body due to the androgen hormones (15), 

PMOS and insulin resistance 

People with PMOS are at higher risk of experiencing insulin resistance (15). Insulin resistance is caused by chronic low-level inflammation that prevents body tissues from taking up and using blood sugar (glucose). This leads to higher blood sugar levels, and extra blood sugar is stored as fat (16). 

PMOS is one of the leading causes of infertility. For people with PMOS and a high BMI, even a small amount of weight loss (around 5% of starting body weight) helps regulate menstrual cycles and restore ovulation. Medications that help improve insulin sensitivity can also improve ovulation (15,17). 

Low body weight and fertility

Low body weight can also impact fertility. Women with an underweight BMI (<18.5) and women who have very low body fat from heavy exercise, illness, or restrictive eating may have differences in hormone levels that affect their ability to become pregnant (18). 

People with low body weight have higher levels of cortisol and lower levels of leptin (19). They often have lower levels of adipose tissue overall. These changes can lower the production of estrogen. Lower estrogen levels disrupt the hormone feedback system in the body, causing irregular periods and preventing ovulation (20).

It may take underweight women longer to become pregnant while TTC (10). Women who are underweight may also have a slightly higher risk for miscarriage (21). Being underweight is also linked to pregnancy risks, including preterm birth and low birth weight (22).

How small changes in weight and lifestyle can help

You deserve to be your healthiest and strongest self, regardless of your body weight or ability to become pregnant. Many of the simple lifestyle shifts that support your fertility are also recommended for overall health. 

These small, consistent, and realistic changes can help you take care of yourself on your fertility journey.

Get regular exercise

Health experts recommend doing at least 150 minutes of moderate-intensity aerobic exercise (like walking, swimming, jogging, or biking) per week (23). They also recommend at least two strength training sessions per week (23). 

Regular exercise helps to reduce body fat, maintain a healthy body weight, and improve heart health, mood, and brain health (24). 

A regular exercise routine will also support positive pregnancy outcomes. During pregnancy, it helps manage discomforts like back pain and constipation. Exercise decreases the risk of pregnancy complications, like gestational diabetes and preeclampsia (25). 

While high levels of intense exercise can interfere with ovulation, most healthy women with regular periods can exercise regularly without affecting their fertility (26).

Avoid tobacco, alcohol, or other substances

Both men and women who are hoping to conceive should avoid alcohol, tobacco, or other substances to improve their chances of becoming pregnant (27). 

Eat a healthy diet 

General dietary recommendations for overall health also apply when trying to conceive. It’s best to cut back on trans fats, sugars, and processed carbohydrates (28). 

Diets that are high in fiber, omega-3 fatty acids, lean protein, fruits, and vegetables are associated with improved fertility outcomes (28). 

The Mediterranean diet pattern is commonly recommended, as it's linked to improved health outcomes for not just fertility, but also heart and metabolic health (28).

Maintain a healthy body weight

Having a body weight within a healthy range is associated with improved pregnancy outcomes(29). 

People who are underweight may slowly gain weight by increasing intake of calorie- and nutrient-dense foods and decreasing excessive vigorous exercise. For women who are overweight or obese, even a 5% reduction in body weight has been shown to improve fertility outcomes (30). Lifestyle changes such as diet and activity adjustments may help someone lose weight and improve their ability to get pregnant (31). 

Weight loss medications may also help manage body weight before pregnancy, but they are not recommended for women who are pregnant or while TTC (32). If you are taking weight loss medication and become pregnant, it’s important to speak to your healthcare provider. 

Male fertility and weight

Women often carry the burden of fertility challenges, but male factors can also play a significant role. High BMI is linked to poor fertility outcomes in men, including low sperm count, longer time to conceive, and infertility (33).

Men with higher BMI may carry more adipose tissue. This tissue converts androgen hormones (like testosterone) to estrogen, which can impact fertility by creating a lower testosterone and higher estrogen environment (34). 

Obesity affects other hormones in the body, like cortisol and insulin. This can alter spermatogenesis (the formation of sperm). Obesity may increase the risk of chronic health conditions that impact sexual function, like cardiovascular disease, diabetes, and erectile dysfunction (34). 

Men who are underweight may have low sperm count and/or semen volume, but more research is needed (35).

When to see a healthcare provider

Some people become pregnant right away when TTC, and for others, it takes time. Fertility is influenced by many different factors beyond body weight.

Consider speaking to your healthcare provider if you (13,29,36):

• Are under 35 years old and have been TTC for one year or longer 

• Are 35 years old or older and have been TTC for 6 months or longer 

• Are 40 years old or older and TTC 

• Have a genetic condition or are a carrier for a genetic condition that may impact family planning

• Have a diagnosis that may impact your fertility, such as irregular periods or endometriosis 

• Have a partner with low sperm count

• Have had multiple miscarriages or pregnancy losses 

What to expect at a fertility appointment

Your fertility care provider will take several visits to fully understand your health history and develop a personalized care plan.

They will review your (1): 

• Medical history, including medical conditions, surgeries, family history, and medication use

• Diet, exercise, substance use, and other lifestyle factors

• Reproductive health history, including pregnancy history, past infections, and any current sexual health symptoms

• Fertility history, including how long you have been TTC, how often you have sex, and what fertility testing you have done so far

Your healthcare provider may recommend blood work to test hormone levels that can affect fertility. They might also recommend an ultrasound of the pelvis. Sometimes, they recommend other procedures that help look at the uterus and fallopian tubes more closely to find potential causes of infertility (1). 

Your provider may perform a physical exam, which can include a pelvic exam. During a pelvic exam, your healthcare provider looks at the vulva and external genitalia. They may place a speculum inside the vaginal canal to look at the vagina and cervix. They may also place fingers of a gloved hand in the vagina to feel the cervix, uterus, and ovaries (37). This gives your provider information about your unique anatomy. 

It is important to know that anyone can decline to have a pelvic exam at any time. Even if the exam has already started, you can always ask your provider to stop the exam. You are in control of your body.

If pelvic exams are difficult for you, there are several ways you can advocate for yourself to feel more empowered (38):

• Bring a trusted support person 

They can hold your hand, stand with you during the exam, and help you advocate for yourself if it feels hard to find your voice.

• Ask to play music or dim the room lighting

Creating a calming atmosphere may put you more at ease.

• Place the speculum yourself

For some people, this provides a sense of control even in a very vulnerable space. You can also ask to use a smaller-sized speculum if you experience discomfort.

• Ask for more communication

Some people find it helpful to clearly signal their needs by using words like "stop" and "pause" during the exam.

Tracking with Clue

Trying to conceive can be complex, and body weight is just one of many factors that may influence fertility. There are still many aspects of fertility we are learning more about, and your ability to become pregnant is not a reflection of your worth.

You can use Clue Conceive to track your cycles and get personalized predictions to time sex or home insemination effectively. This can offer a greater sense of insight and structure during a process that often feels uncertain. Tracking can also give you data to bring to a trusted healthcare provider, supporting more informed conversations about your fertility journey. 

You don’t need to walk your fertility journey alone.

FAQs

Can I get pregnant if I’m overweight?

Yes, people of all body weights may become pregnant and deliver healthy babies (39). However, people who are overweight or obese may take a longer time to conceive. Obesity may increase the risk of clinical infertility and miscarriage (10,12). 

How much weight loss helps fertility?

Research shows that a 5% weight loss helps to improve fertility outcomes (30). This may help make periods more regular, and it may also increase ovulation and conception rates (30). 

Does male weight affect fertility?

Yes, weight can also affect male fertility. Being both underweight and overweight can have an impact. Low BMI may be associated with low sperm count and low semen volume, while high BMI may be linked with low sperm count, longer time to conceive, and infertility (33). 

Are fertility treatments less effective with high BMI?

Research has shown that a high BMI can affect fertility treatment response, even in the absence of any other risk factors (11). People with high BMIs (both overweight and obese) may require longer courses of ovarian stimulation treatments. They may also have lower rates of clinical pregnancy overall after fertility treatment. People with obesity may have less successful egg retrievals (11). 

High BMI does not seem to affect rates of miscarriage or live birth rates for people who undergo fertility treatments (11). 

Is BMI the only measure that matters? 

No, while BMI is commonly used, other measures of metabolic health can also be important for reproductive health. 

For example, waist circumference is linked with increased risk of infertility, independent of BMI (40). One study found that for each centimeter increase in waist circumference, the risk of infertility increased by 3% (40). This may be because central belly fat can impact inflammation and hormone levels, leading to changes in ovulation and hormone balance. However, more research is needed to fully understand this link. 

Newer research has also attempted to find a link between relative fat mass (RFM) and fertility (41). RFM is a measure of your percentage of body fat, and it aims to take body composition (fat vs. muscle) into account. In some women, higher RFM may be linked to infertility, but more research is needed (41).