Hum. Reprod. Advance Access published online on October 14, 2009
Human Reproduction, doi:10.1093/humrep/dep360
An internet-based prospective study of body size and time-to-pregnancy
1 Department of Epidemiology, Boston University School of Public Health, Boston, MA, USA 2 Slone Epidemiology Center, Boston University, 1010 Commonwealth Ave, 4th floor, Boston, MA 02215, USA 3 RTI Health Solutions, Research Triangle Park, Durham, NC, USA 4 Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark
5 Correspondence address. E-mail: lwise{at}bu.edu
BACKGROUND: Recent studies have shown that both female and male obesity may delay time-to-pregnancy (TTP). Little is known about central adiposity or weight gain and fecundability in women.
METHODS: We examined the association between anthropometric factors and TTP among 1651 Danish women participating in an internet-based prospective cohort study of pregnancy planners (2007–2008). We categorized body mass index (BMI = kg/m2) as underweight (<20), normal weight (20–24), overweight (25–29), obese (30–34) and very obese (
35). We used discrete-time Cox regression to estimate fecundability ratios (FRs) and 95% confidence intervals (CI), controlling for potential confounders.
RESULTS: We found longer TTPs for overweight (FR = 0.83, 95% CI = 0.70–1.00), obese (FR = 0.75, 95% CI = 0.58–0.97), and very obese (FR = 0.61, 95% CI = 0.42–0.88) women, compared with normal weight women. After further control for waist circumference, FRs for overweight, obese, and very obese women were 0.72 (95% CI = 0.58–0.90), 0.60 (95% CI = 0.42–0.85) and 0.48 (95% CI = 0.31–0.74), respectively. Underweight was associated with reduced fecundability among nulliparous women (FR = 0.82, 95% CI = 0.63–1.06) and increased fecundability among parous women (FR = 1.61, 95% CI = 1.08–2.39). Male BMI was not materially associated with TTP after control for female BMI. Compared with women who maintained a stable weight since age 17 (–5 to 4 kg), women who gained 15 kg had longer TTPs (FR = 0.72, 95% CI = 0.59–0.88) after adjustment for BMI at age 17. Associations of waist circumference and waist-to-hip ratio with TTP depended on adjustment for female BMI: null associations were observed before adjustment for BMI and weakly positive associations were observed after adjustment for BMI.
CONCLUSIONS: Our results confirm previous studies showing reduced fertility in overweight and obese women. The association between underweight and fecundability varied by parity.
Key words: fertility/obesity/body mass index/prospective study/cohort study
Submitted on May 15, 2009; resubmitted on August 19, 2009; accepted on September 9, 2009.