Long-term fracture risk among infertile women: a population-based cohort study.

Nulliparity has been linked to bone loss and fractures, but the contribution of infertility is unclear. The purpose of this study was to assess the long-term risk of fractures among infertile women. In a population-based retrospective cohort study, all 658 Olmsted County, Minnesota, women with infertility (failure to conceive after 1 year despite intercourse without contraception) first diagnosed at Mayo Clinic in 1935-1964 were followed for fractures. Risk was assessed by comparing new fractures of each type to the number expected from sex-specific and age-specific fracture rates in the general population (standardized incidence ratios [SIR]). During 18,130 person-years of follow-up, 184 women experienced at least one fracture when 291 would have been expected on the basis of fracture incidence rates in the general population (SIR 0.6, 95% CI 0.5-0.7). There was no increase in proximal femur fractures (SIR 1.0, 95% CI 0.6-1.6) and a statistically significant decrease in the risk of distal forearm fractures (SIR 0.7, 95% CI 0.5-0.97), two of the three sites traditionally associated with osteoporosis. By contrast, there was a significant increase in subsequent vertebral fractures (SIR 1.9, 95% CI 1.4-2.4) that was consistent across divergent causes of infertility and reported menstrual patterns. Although an apparent increase in the risk of vertebral fractures requires further investigation, we saw no indication of an increase in limb fractures, suggesting that infertility does not have long-term adverse skeletal effects like those reported for athletes and dieters with irregular menses.