Trying to Conceive: Will Low Body Fat Level Affect My Ability to Get Pregnant?

My husband and I would like to start a family this year. I am a very healthy 31-year-old. I get a lot of exercise and eat a balanced diet. My concern is with my weight and body fat level. I am 5'7 inches tall and weigh 123 pounds. My body fat is about 17 percent. I have heard that body fat should be 18 percent or higher to get pregnant. Is this true?

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Peg Plumbo CNM

Peg Plumbo has been a certified nurse-midwife (CNM) since 1976. She has assisted at over 1,000 births and currently teaches in the... Read more

Body weight, specifically body fat, plays an essential role in the initiation and maintenance of reproductive function of women. Moreover, once pregnancy occurs, the existing amount of body fat at conception, and the weight gain during pregnancy, appear to influence pregnancy outcome.

Some women with minimal body fat have no menstrual periods or are very irregular. About six percent of cases of primary infertility in which there is a problem with ovulation result from being excessively underweight. More than 70 percent of these women conceive spontaneously if their weight disorder is corrected through weight gain. If a woman weighs less than 95 percent of predicted ideal body weight for height, it is recommended that she be counseled to increase her weight to ideal levels.

Body fat affects release of the hormones which stimulate the ovary to produce an egg and regulate the menstrual cycle. When body weight is within five percent of the ideal body weight, these hormones are generally returned to normal and ovulatory cycles resume.

Underweight women have a propensity to convert normal estrogen to a more "anti-estrogen" type. And these same women do not always respond to Clomid therapy to induce ovulation because Clomid requires the correct type of estrogen in order to work.

If your cycles are regular and you are ovulating, you should have no difficulty conceiving and carrying a pregnancy to term at your weight. At 123, you are at the lower, but still normal, range for your height and not at the "less than 95 percent" category. In Toni Weschler's book, "Taking Charge of Your Fertility," she states that for women to maintain normal ovulatory cycles, they should have a minimum of 18 percent body fat. This is no way implies that you cannot get pregnant or maintain a pregnancy if you have less body fat.

In my experience, it is the women who lose weight (up to one-third of their total weight) or begin strenuous athletic training who have problems with infertility -- primarily because it causes them to cease ovulating.

Try not to worry. I would recommend that you go ahead and try to conceive. After one year, if you have not conceived, I would take your charts to a reproductive endocrinologist for help.

I hope you are able to conceive and I wish you the best.

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