Does Your Body Mass Index (BMI) Affect Your Fertility?

BMI fertililty

If you are pregnant and you want to be pregnant, consider yourself fortunate. For about one out of ten women, getting pregnant or staying pregnant is a real problem. There are many causes for infertility, but one of the biggest problems is reversible. It’s your weight. It could be because you are overweight or it could be because you are underweight. Both problems contribute to infertility.

Weight may be a problem for someone you know who is struggling to get pregnant. If you are pregnant now, a big change in your weight could be a problem for future pregnancies. The big link between infertility and weight is ovulation. If your basal metabolic index (BMI) is too high or too low, ovulation is affected. You can find a BMI table on the internet. You plug in your height and weight to get a number. Under 19 is underweight. Over 24 is overweight. Sex hormones responsible for ovulation are stored in fat cells. Too much or too little fat can cause infertility.


Being underweight keeps you from ovulating normally. Ovulation is the production and release of an egg from your ovary. A big warning for an ovulation problem is having irregular periods. If you become very underweight, you may stop having periods. You may also have shrinking of your breasts and vaginal dryness. If your BMI drops below 17, it could be a signs of an eating disorder like anorexia or bulimia.

High BMI

Infertility from being overweight is more common. You may also have irregular periods. A high BMI may be a sign of another big cause of infertility called polycystic ovary syndrome (PCO). PCO can cause insulin resistance, which means you have trouble using sugar for energy. The sugar goes into fat cells. PCO is commonly linked to obesity and infertility.

High BMI can cause many problems with pregnancy. It can make it harder to get pregnant with assisted reproductive technologies like artificial insemination and in vitro fertilization. You are also at higher risk if you get pregnant. These risks include a higher risk for high blood pressure, gestational diabetes, and C-section.

What to Do

The answer is simple, getting to a healthy weight will help. Not that it is easy to lose weight, but studies show that losing as little as 5-10 percent of your weight helps fertility. Putting on some pounds if you are underweight can restore normal periods and ovulation.

And don’t let your partner off the hook. Did you know that the cause of infertility is just as often the man’s fault as the woman’s? Men who are overweight or obese may produce less sperm and more abnormal sperm. Low testosterone – a common cause of male infertility – can be caused by obesity. Men with low testosterone are also more likely to be overweight. Symptoms include low sex drive and erectile dysfunction. Losing weight helps men with low testosterone.

If you are overweight or underweight, talk to your doctor. Work together on a safe plan to get back to a healthy weight. Your plan should include diet and lifestyle changes, but not a crash diet. Rapid weight loss can make infertility worse. If you have a BMI over 40, weight loss surgery –bariatric surgery – may be an option to talk about.

Christopher Iliades
Dr. Chris Iliades is a medical doctor with 20 years of experience in clinical medicine and clinical research. Chris has been a full time medical writer and journalist since 2004. His byline appears in over 1,000 articles online including EverydayHealth, The Clinical Advisor, and Healthgrades. He has also written for print media including Cruising World Magazine, MD News, and The Johns Hopkins Children's Center Magazine. Chris lives with his wife and close to his three children and four grandchildren in the Boston area.

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