Can weight impact your ability to get pregnant?

Can weight impact a woman or man's ability to conceive? And what about the effects a mother's obesity has on her fetus? In part two of a special series on “Today” called “Living Large in America,” NBC News medical editor Dr. Nancy Snyderman and guests look at these questions and more. Dr. Clarissa Gracia was invited to discuss this topic on the show, and here she writes more on the subject:

Obesity has reached epidemic proportions in this country, with 31 percent of white, 38 percent of Hispanic, and 49 percent of African American women considered overweight or obese (2002 Statistics). Obesity is defined as a body mass index (BMI) greater than 30kg/m2 while overweight is defined as a BMI of 25 –30 kg/m2. ( Calculate your body mass index here. )

Obesity has been linked to multiple medical problems including infertility. Infertility in obese and overweight women is primarily related to ovulatory dysfunction. Anovulation often results in irregular menstrual cycles. Indeed, studies have shown that 30 percent to 47 percent of obese women will have irregular menstrual cycles. The likelihood of irregular menstrual cycles increases in direct proportion to increases in weight. Furthermore, it has been demonstrated that weight reduction often leads to resumption of normal menses and increased pregnancy rates.

Polycystic ovary syndrome (PCOS) is a specific medical condition associated with irregular menstrual cycles, anovulation, obesity and elevated levels of male hormones. While some obese women have PCOS, many do not have this condition. In addition to anovulation, there may be other mechanisms by which obesity interferes with the ability to achieve pregnancy. For example, in one study, it took obese women undergoing intrauterine inseminations with donor sperm longer to conceive than normal weight women. There is limited data that obesity negatively affects male fertility as well. Hormonal changes in obese men and increased scrotal temperature are potential underlying causes of impaired semen parameters.

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What can women do?
First line treatment for obesity-related infertility is weight loss and lifestyle modification. While any amount of weight loss in obese women may improve fertility, a loss of 5 percent to 10 percent in overall body weight can result in spontaneous ovulation in 60 percent of patients. Efforts should be made to restrict calories to 1000 to 1200kcal/day, and to exercise at moderate intensity for at least 30 minutes, three times a week. Participation in a formal weight loss program can be very helpful. Weight loss medications and bariatric surgery (gastric bypass or gastric banding) may be recommended as well, if lifestyle modifications fail to result in sufficient weight loss.

Apart from weight loss, treatments for infertility in obese women do not differ substantially from treatments in non-obese women. For anovulation, first line treatment generally consists of ovulation induction with oral medications such as clomiphene citrate. Women who fail to achieve pregnancy with oral medications are often treated with injectable ovulation induction agents such as recombinant or urinary gonadotropins. In vitro fertilization is often performed if these treatments fail or if there are other factors contributing to infertility.

It has been shown that obesity is associated with a longer duration of treatment, increased dosage of medication, and an increased risk of treatment cancellation due to poor response. Studies have also shown that pregnancy rates are approximately 30 percent lower in obese women undergoing IVF compared to women of normal weight. It has been proposed that the IVF is less successful for several reasons. Some of these include impaired absorption of medication due to increased fat stores, limited ability to visualize ovaries during ultrasound monitoring, and more challenging egg retrieval.

Moreover, once pregnancy occurs, obese women have a higher rate of pregnancy loss. In fact, studies show they have up to a two-fold higher risk of miscarriage compared to normal weight women. It is not clear why this occurs. Nonetheless, weight loss can dramatically decrease the risk of miscarriage.

The bottom line:
Obesity is a major health problem that is associated with infertility and miscarriage. Weight loss is extremely valuable in the management of such patients and can enhance fertility and decrease miscarriage rates.

Dr. Clarissa Gracia is a reproductive endocrinologist at the University of Pennsylvania Penn Fertility Care Center.