If you've been struggling to get pregnant, the problem might be your weight. That's the case with about 1 of every 10 couples facing infertility. It could be because you're overweight. Or, it could be because you're underweight. Both problems can affect your fertility. The best way to know if you are over or under your healthy weight is to check your body mass index (BMI). You can do this using a special BMI calculator on the website of the Centers for Disease Control and Prevention. Just enter your height and weight. The number you get will be your BMI. A number lower than 18.5 means you are underweight. A number 25 or higher is overweight. How your weight affects your fertility has to do with how your sex hormones are stored in fat cells. Too much or too little fat can cause infertility. Weight and Female Infertility Women who are underweight may not be able to ovulate normally. Ovulation is the production and release of an egg from the ovary. One sign of a problem with ovulation is having irregular periods. Women who are very underweight may stop having periods. They may also have shrinking of their breasts and vaginal dryness. Women who are overweight have more problems with ovulation. They may have irregular periods. They also are more likely to have one of the most common causes of infertility—a condition called polycystic ovary syndrome (PCOS). PCOS can cause insulin resistance. Insulin is the hormone you need to use sugar for energy. Insulin resistance can contribute to weight gain and obesity. Being overweight also can make it harder to get pregnant with procedures like artificial insemination and in vitro fertilization. In addition, overweight and obesity increases the risk of complications of pregnancy. These include high blood pressure, diabetes and the need for a C-section. Weight and Male Infertility The main cause of infertility in men is a low sperm count. Men who are overweight or obese may produce fewer sperm and more abnormal sperm. Men who are overweight are more likely to have low testosterone. That goes both ways: Men with low testosterone are more likely to be overweight. Symptoms of low testosterone include a low interest in sex and trouble getting an erection. These problems can make pregnancy less likely. Achieving a Healthy Weight If you are overweight or underweight, talk with your doctor about a plan to get back to a healthy weight. Studies show that losing as little as 5 to 10% of your weight—if you're overweight—helps fertility. Losing weight also can help men with low testosterone. Gaining weight for underweight women can restore normal periods and ovulation. If you are overweight, the plan should include diet and lifestyle changes. Avoid crash diets. These can make infertility worse. For women with a BMI over 40, weight loss surgery may help overcome infertility. For advice and help achieving a healthy weight, search Healthgrades.com for a doctor in your area. Focus your search on providers who specialize in weight management or reproductive (fertility) medicine.