Smoking is associated with an increased risk of fractures in women after childbirth: a nationwide population-based cohort study in Finland

Background and purpose — Smoking weakens bone health and increases the risk of fractures. We investigated the incidence of fractures in smoking, fertile-aged women and compared it with that of non-smoking, fertile-aged women using data from nationwide registers. Patients and methods — We conducted a retrospective register-based nationwide cohort study from 1998 to 2018. We identified all women smoking during pregnancy from the Medical Birth Register and compared these with non-smok-ers. We gathered fractures for both groups from the Care Register for Health Care. Pregnancies with missing smoking or socioeconomic status were excluded. A Cox regression model was used to analyze adjusted hazard ratios (aHR) with 95% confidence intervals (CI) for fractures during the 5-year follow-up starting from delivery. The model was adjusted for the age of the mother at the time of delivery and socioeconomic status. Results — The smoking group included 110,675 pregnancies and the non-smoking group 628,085 pregnancies. The overall fracture rate was higher in smokers after 1-year follow-up (aHR 1.7, CI 1.5–2.0) and 5-year follow-up (aHR 1.7, CI 1.6–1.8). After 5-year follow-up, the fracture rates for polytraumas (aHR 2.3, CI 1.4–3.7), inpatient admitted fractures (aHR 2.0, CI 1.7–2.4), and non-admitted fractures (aHR 1.8, CI 1.7–1.9) were all higher among smoking women. Conclusion — Smoking in fertile-aged women was associated with a higher risk of fractures during the 1-year and 5-year follow-up after giving birth, also after adjusting for age and socioeconomic status. Whether the increased fracture risk is caused by direct effects of smoking on bone health or riskier behavior remains uncertain.