Weight and Fertility

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Weight and Fertility

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How do I determine if I am at the optimal weight to become pregnant?

One of the easiest ways to determine if you are underweight or overweight is to determine your Body Mass Index (BMI). There are many tables available online (search term: BMI table). You will need to enter your height and weight to calculate your BMI. (The tables will convert your height and weight into kilograms and meters and will then express BMI as kg/m2).

What is a normal BMI?

A BMI between 19 and 24 is considered normal; less than 19 is considered underweight. A BMI between 25 and 29 is considered overweight and greater than 30 places you in the category of obese.

How does BMI affect fertility?

Many women in the underweight, overweight, and obese categories will not have a problem becoming pregnant. But women who are not an ideal body weight may have problems with ovulation. This could lead to problems with fertility.

A BMI of 18.5 or less (underweight) may cause irregular menstrual cycles and may cause ovulation (release of an egg from the ovaries) to stop. A BMI of 17.5 or less may indicate an eating disorder. Women at less than normal BMI should talk with their doctor about exercise, nutritional or hormonal issues.

A BMI in the obesity range may also lead to irregular menstrual cycles and irregular ovulation. Women with a BMI of greater than 29 should see a doctor for an evaluation of hormonal status related to ovulation. A preconception visit can also help identify other obesity-associated disorders that impact pregnancy. They include possible thyroid disease, insulin resistance, or Type 2 diabetes. Obese women who have normal ovulation cycles still have lower pregnancy rates than normal weight women.

Does obesity affect the chance of getting pregnant with treatment and having a healthy baby?

Although not all reports agree, there is evidence that obesity lowers the success rates of in vitro fertilization (IVF). In some studies, there has also been a higher rate of pregnancy loss (spontaneous miscarriage) in obese women. In obese women, there is an increasing amount of evidence that many complications of pregnancy for the mother (gestational diabetes, preeclampsia,) and her baby (birth defects) are increased. In addition, obese women have an increased chance of a cesarean section for delivery.

Are there fertility problems in men with obesity?

Obesity in men may be associated with changes in testosterone levels and other hormones important for reproduction. Low sperm counts and low sperm motility have been found to occur more often in overweight and obese men.

What can I do to achieve a normal BMI if I am in the obese category?

You should see a doctor. The doctor will consider all factors including your age and other possible infertility factors and then make a recommendation about whether you should try to lose weight before you try to get pregnant. Changing your diet and lifestyle (for example, exercise) is often the first treatment plan. Women with more severe obesity may be candidates for medical therapy. Weight loss surgery (bariatric surgery) is the most effective treatment for weight loss in women with a BMI greater than 40.

If I have been told that I have infertilty related to Polycystic Ovarian Syndrome (PCOS), is there any additional treatment I can try?

PCOS is a very common condition in young women (approximately 8% to 10%). Not all women with PCOS are overweight or obese, but many PCOS women have signs of insulin resistance and/or obesity. A low calorie diet and exercise may lead to weight loss, regular menstrual cycles, and ovulation.

Revised 2011 

Weight and Fertility-pdf

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