Association between pregravid physical activity and family history of stroke and risk of stillbirth: population-based cohort study

OBJECTIVES: To evaluate whether family history of disease and pregravid lifestyle and cardiovascular risk factors are associated with subsequent stillbirth delivery. DESIGN: Prepregnancy cohort study. SETTING: Cohort Norway regional health surveys (1994–2003) linked to Medical Birth Registry of Norway for deliveries through 2012. PARTICIPANTS: 13 497 singleton births (≥22 weeks gestation) in 8478 women. MAIN OUTCOME MEASURE: Risk of stillbirth evaluated by Poisson regression. RESULTS: Mean (SD) length of follow-up was 5.5 (3.5) years. In analyses adjusting for baseline age and length of follow-up, ≥3 hours of baseline past-year vigorous physical activity per week (resulting in shortness of breath/sweating) was associated with increased risk of stillbirth compared with <1 hour/week of vigorous activity (incidence rate ratio, IRR 2.46; 95% CI 1.23 to 4.90). In contrast, baseline past-year light physical activity of ≥3 hours per week associated with reduced risk of stillbirth compared with <3 hours of light physical activity per week (IRR 0.53; 95% CI 0.30 to 0.93). A family history of stroke associated with increased risk of stillbirth delivery (IRR 2.53; 95% CI 1.06 to 6.01). Because overweight/obese women may experience shortness of breath and sweating with less physical exertion than normal weight women, a sensitivity analysis was conducted limited to women with a normal BMI (≥18.5 and <25 kg/m(2)). Vigorous activity of ≥3 hours per week (IRR of 4.50; 95% CI 1.72 to 11.79) and a family history of stroke (IRR of 3.81; 95% CI 1.31 to 11.07) were more strongly related to stillbirth risk among women with a normal BMI than that observed for all women combined. Established risk factors also associated with stillbirth risk. CONCLUSIONS: The study identified physical activity and family history of stroke as potential new risk factors for stillbirth delivery.