Endocrine Today, October 2017

Many adolescents and young adults may believe that obesity-related diseases, such as heart disease, diabetes and osteoarthritis, are concerns of old age. But excess weight can have detrimental effects on fertility, a consequence younger adults may not recognize until they want to start a family.

Although age is the greatest predictor of fertility among women, obesity has a substantial effect on the likelihood of pregnancy. For example, the likelihood of pregnancy may be similar between a young woman with BMI greater than 30 kg/m2and a woman aged older than 35 years, according to Nanette Santoro, MD, the E. Stewart Taylor Endowed Chair in the department of obstetrics and gynecology and professor in the division of reproductive endocrinology at the University of Colorado Denver Anschutz Medical Campus

“So, if she were 25 years old, she would have the fertility of a woman approaching 40 years, in her ability to get pregnant per month,” Santoro told Endocrine Today.

Obesity has effects throughout the hypothalamic-pituitary-gonadal axis in both men and women, according to Rhoda H. Cobin, MD. Source: Jean Whiteside Photo; printed with permission.

Further, “there is a 3% drop in monthly fecundability for each BMI unit above 25 kg/m2. So, for a woman with a BMI of 35 kg/m2, she has a 30% drop in her fertility by this measure,” she said. “There is a ‘dose-response’ relationship — the greater the obesity, the more likely the infertility.”

Obesity affects not only fecundability — the probability of pregnancy in a given month — but it also is associated with increased risk for spontaneous abortion, congenital anomalies, gestational diabetes and preeclampsia, according to a 2015 American College of Obstetricians and Gynecologists (ACOG) Obesity in Pregnancy Practice Bulletin. Risk for stillbirth, although low, is increased by 30% for women with BMI 30 kg/m2 to 34.9 kg/m2 and almost doubles with BMI 40 kg/m2and higher, according to the bulletin.

Maternal obesity may also affect the long-term health of children, elevating their risks for metabolic syndrome and childhood obesity, according to ACOG. However, separating prenatal effects from influences after birth is difficult.

Obesity is not a concern only for women; men with obesity may also have decreased fertility.

“We tend to think of this as a women’s issue, but it actually takes two people to make a baby,” Rhoda H. Cobin, MD, clinical professor of medicine in the division of medicine, endocrinology and bone disease at the Icahn School of Medicine at Mount Sinai School, told Endocrine Today. “Obesity affects men’s fertility as well as women’s fertility, so when people talk about infertility, they’re really talking about a couple.”