In a first of its kind study, researchers from the Slone Epidemiology Center (SEC) at Boston University (BU) found that African-American women who were overweight or obese had a greater risk of delayed conception and infertility when compared with women who were of normal weight. In addition, women who had larger waist circumferences and greater waist-to-hip ratios (i.e., apple-shaped women) had lower fertility. These findings of time to pregnancy (TTP) are published online in Human Reproduction.
“This study is important because it contributes new data on predictors of infertility in black women and suggests that both central and overall obesity are important factors influencing pregnancy rates,” said lead author, Lauren Wise, ScD, senior epidemiologist at SEC and associate professor of epidemiology at Boston University School of Public Health. “Given the small number of studies on central obesity and fertility, this study makes an important contribution to scientific literature. She noted that mechanisms to explain the findings could involve obesity-related hormonal changes and disturbances in the menstrual cycle.
Based on the Black Women’s Health Study (BWHS), the largest ongoing follow-up study of black women in the U.S., eligible women aged 21-40 years reported at least one planned pregnancy attempt during 1995-2011. Height and weight were reported in 1995, with weight updated every two years; waist and hip circumferences were reported in 1995 and updated in 2003. In 2011, women reported how long it took them to conceive each pregnancy.
During 1995-2011, there were 2,239 pregnancy attempts reported by 1,697 women, resulting in 2,022 births. The study found that high BMI was associated with delayed conception: relative to BMI 18.5-24.9 (normal weight), the risks of becoming pregnant were 7 percent, 8 percent and 27 percent lower for women who were overweight (BMI 25-29), obese (BMI 30-34), or very obese (BMI≥35), respectively. After taking into account BMI, women with large waist circumferences (≥33 inches) and large waist-to-hip ratios (≥0.85) also experienced delays in conception.
Led by researchers at the SEC, the BWHS has followed 59,000 African-American women through biennial questionnaires since 1995 and has led to a better understanding of numerous health conditions that disproportionately affect African-American women.
Funding for this study was provided by the National Cancer Institute under grant award # CA058420. Co-authors of the study include Lynn Rosenberg, ScD, principal investigator of the BWHS and professor of epidemiology at BUSPH, and Julie R. Palmer, ScD, professor of epidemiology at BUSPH.
The study’s lead author, Lauren A. Wise, ScD, is also principal investigator of the Boston University PREgnancy STudy Online (PRESTO), which recently began recruitment for an internet-based study of female pregnancy planners in Massachusetts. If you would like to enroll in this study, visit: http://presto.bu.edu.