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/m2). 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.