Being overweight can affect your fertility and increase the chance of complications during pregnancy. Women who are overweight tend to have irregular menstrual cycles and ovulation and are thus less likely to get pregnant both through natural conception and assisted reproduction. If you’re overweight, getting to a healthy weight can improve your chances of getting pregnant. In this factsheet, you’ll learn how exactly weight and fertility are linked and get some tips on leading a healthy lifestyle.
Body fat is difficult to measure directly and is often calculated according to Body Mass Index (BMI). Your BMI is your body weight in kilograms divided by your height in meters squared. According to the World Health Organization (WHO), people with a BMI equal to or greater than 25 kg/m2 are overweight, and those with a BMI equal to or greater than 30 kg/m2 are obese. But BMI doesn’t account for differences in your frame, lean body mass, nor how body fat is distributed, i.e. being pear shaped or apple shaped. This is important because having more fat around the stomach area can cause higher metabolic risk.
Metabolic risk is a group of risk factors raising the likelihood that you will get heart disease or other health problems like diabetes or stroke, a group of conditions called metabolic syndrome. The term “metabolic” refers to your body’s processes that help it work as it should. Risk factors are traits, conditions, or habits that increase your chance of developing a disease.
All of the metabolic risk factors are closely linked to being overweight or obese and how physically active you are. Having 3 metabolic risk factors leads to a diagnosis with this metabolic syndrome.
Here are the risk factors:
- Excess fat around your stomach (apple shaped)
- A high level of triglyceride fats circulating in your blood
- A low level of high-density lipoprotein cholesterol levels (good fats)
- High blood pressure
- High fasting blood sugar levels
If you are taking medication to treat heart disease, diabetes or stroke, you are also at risk.
But you can prevent or delay metabolic syndrome by making healthy lifestyle choices, which we talk more about later.
Obesity reduces fertility by interfering with the body’s hormones. According to the American Society for Reproductive Medicine (ASRM), obesity is the reason for infertility in 6% of women who are struggling to conceive and have never been pregnant.
Many studies have found that being overweight or obese leads to menstrual cycle irregularities. This is because a carefully timed interplay of hormones controls your reproductive cycle, and being overweight can disrupt your hormonal levels. When your body has excess fat, you have lower levels of the key sex hormones, luteinizing hormone (LH) and follicle stimulating hormone (FSH). Low levels of LH and FSH interfere with the ovaries: they can’t release an egg each month as they should, which can cause infertility.
Obesity also converts androgens (male sex hormones) to estrogens in fatty tissue. Too much estrogen can lead to irregular cycles and anovulation (not ovulating).
Furthermore, excess weight, particularly around your stomach, is associated with insulin resistance. Insulin is a hormone made in your pancreas, which tells the cells to absorb sugars (glucose) from your blood. But when the body gets resistant to insulin, you need to make more and more of it to keep blood sugars low. This can lead to diabetes and having higher androgen levels, which is called hyperandrogenemia.
Hyperandrogenemia is the main symptom of polycystic ovarian syndrome (PCOS), a condition where cysts may grow on the ovaries and a hormonal imbalance gets in the way of ovulation. 40 to 50% of women with polycystic ovarian syndrome have insulin resistance, especially obese women.
PCOS is one of the most common causes of infertility and has a number of negative effects on a woman’s health. Besides irregular periods and ovulation, women with PCOS often have excessive hair growth on their arms, legs and face, dark skin patches, acne, and weight gain. Other health problems that can come from PCOS are sleeping issues, heart disease, mood disorders, and over-thickening of the uterine lining (the endometrium), which can affect implantation of a fertilized egg.
Lastly, being overweight also brings a greater risk of pregnancy complications. Miscarriage becomes more likely, both when you conceive naturally or through assisted reproduction. A study including women who conceived naturally found that obese women were 1.3 times more likely to have a pregnancy loss. This is because obesity can lead to a number of other pregnancy complications, including high blood pressure and diabetes during pregnancy (gestational diabetes), which increase the risk for miscarriage in the first trimester. Other health risks during pregnancy due to a high BMI include blood clots, premature birth, stillbirth, birth defects, and needing an emergency C-section. All in all, there are many reasons to stay active and maintain a healthy BMI. Not just to improve your fertility, but to protect your overall health and that of your future baby.
Having a higher BMI can also lower the chances of success of fertility treatments because of the influence your weight has on:
- Responsiveness to ovarian stimulation, and
- Egg quality
Firstly, having excess fat around your stomach or a higher BMI means your ovaries aren’t as likely to release an egg during ovulation when given fertility treatments such as clomiphene citrate. Overweight women are also less responsive to hormonal treatments meant to cause superovulation (when the ovaries release more than one egg per cycle). Obese women need higher doses of gonadotropins and produce fewer follicles per treatment. Several studies show that women undergoing assisted reproductive treatments need to be treated with gonadotropin hormones over a longer period of time, and IVF cycles are more likely to be cancelled because no eggs can be retrieved.
Secondly, obesity negatively impacts egg quality by altering the follicular environment. This is because obesity changes insulin levels, inflammatory markers, and free fatty acids in the tightly packed cells surrounding the egg in the ovary.
Having a healthy BMI is helpful for family planning. To have good chances of getting pregnant and having a healthy pregnancy, aim for a BMI between 18.5 and 24.9. If your BMI is over 30, even bringing it down a couple points can go a long way. By incorporating some new habits into your daily life, you can get to a healthy weight and improve your fertility.
The first step to losing weight is to look at what you eat. Switch out fatty, processed foods with fresh fruits and vegetables and lean protein. You may find it helpful to get a cookbook for low-calorie recipes. If you notice that you often snack when you’re not actually hungry, reflect on why you have the urge to eat, and replace it with another activity like going for a walk, reading, or calling a friend. And when you do need a little snack, make it healthy: hummus and carrots, mixed nuts, and greek yoghurt with berries all make delicious (and nutritious!) bites in between meals.
Second, start a workout routine. Whether that means joining a local gym, exercising in a park nearby or with at-home videos, aim to get at least 150 minutes of physical activity per week to reach your weight loss goals. It can also help to have a workout buddy to stay motivated. And if there are days where you really don’t feel like it, don’t be too hard on yourself and remember that tomorrow is a new day.
Reducing your calorie intake and getting more active will decrease your metabolic risk and up chances of conceiving. Studies have shown that women with a higher BMI who lose weight are even more likely to get pregnant through assisted reproduction treatment and also need fewer fertility treatments. Not to mention the reduced risk of complications during pregnancy.
Sometimes, medications for weight loss can be helpful when combined with lifestyle changes, especially for people who have tried to lose weight in the past but had difficulty with it. These drugs usually work by suppressing your appetite. But they should be prescribed and taken with caution due to increased risk for high blood pressure and high pulse rate, or increased levels of the hormone serotonin in your body. Doctors also don’t fully understand the impacts of these medications on fertility. So to be on the safe side, it’s best to stick with natural weight loss methods to help your chances of getting pregnant.
If you are having a hard time getting pregnant and are overweight, keep in mind that weight and fertility are closely linked. Having a higher BMI interferes with your cycle and ovulation, reduces the chances of success of fertility treatments, and increases the risk for pregnancy complications such as miscarriage and stillbirth. To protect your health and improve your fertility, set the goal to eat a low-cal diet and exercise a few times per week. Your body and future baby will thank you!
World Health Organization. Preventing and managing the global epidemic Report of the World Health Organization on obesity. Geneva: World Health Organization; 1997. [Google Scholar]
Obesity and reproduction: a committee opinion (asrm.org). Practice Committee of the American Society for Reproductive Medicine. Accessed 8th of December 2021.
Metabolic Syndrome | NHLBI, NIH. National Heart, Lung and Blood Institute. Metabolic Syndrome. Accessed 10th December 2021.
Eunice Kennedy Shriver National Institute of Child Health and Human Development – NICHD (nih.gov). US Department of Health and Human Services, National Institute of Health. Polycystic Ovary Syndrome (PCOS). Accessed 10th December 2021.
Serotonin syndrome – Symptoms and causes – Mayo Clinic. Patient Care and Health Information. Serotonin Syndrome, Mayo Clinic. Accessed 11th of December 2021.
Overweight and fertility when planning a pregnancy. Tommy’s. Accessed 27th of January 2022.
Özcan Dag Z and Dilbaz B: Impact of obesity on infertility in women. J turk Ger Gynecol Assoc. 2015; 16(2): 111-117.
Raj Ghimir P et al: Association between obesity and miscarriage among women of reproductive age in Nepal. PLoS One. 2020; 15(8): e0236435.
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