Major Risk Factors for Stillbirth in High-Income Countries: A Systematic Review and Meta-Analysis

Risk factors for stillbirth have been extensively investigated in the past 2 decades, with increasing emphasis on those that are potentially avoidable. Use of strategies that target potentially avoidable or preventable risk factors could achieve reduction in stillbirth rates. This systematic review of the medical literature was conducted to identify important risk factors for stillbirth in high-income countries that could be potentially reduced through lifestyle or medical intervention. Data from population-based studies published between 1998 and 2009 were obtained by search of several databases, including Medline, CINAHL, and Cochrane Database of Systemic Reviews. The contribution of important modifiable risk factors for stillbirth was estimated for the 5 high-income countries (Australia, Canada, Netherlands, United Kingdom, and United States) having the highest numbers of stillbirths and all relevant data required for analysis. The population-attributable risk (PAR) was calculated for each risk factor identified. Among the 6963 studies identified in the initial review, 96 population-based studies were included after full review. Across the 5 countries, the highest ranking modifiable risk factors were maternal overweight and obesity (body mass index >25 kg/m2); prevalence of overweight and obesity ranged from 28% to 58%, with PARs of around 8% to 18% contributing to around 8000 stillbirths (≥22 weeks' gestation) annually. Two other important modifiable risk factors, advanced maternal age (>35 years) and maternal smoking, had PARs of 7% to 11% and 4% to 7%, respectively, and contribute annually to more than 4200 and 2800 stillbirths, respectively. Maternal smoking is estimated to contribute to approximately 20% of stillbirths in disadvantaged populations (indigenous Australian and Canadian women). The contribution of primiparity to stillbirths is estimated to be around 15%. Among pregnancy disorders, small size for gestational age and placental abruption have the highest PARs (23% and 15%, respectively). Other important risk factors associated with stillbirth in high-income countries include preexisting diabetes and hypertension. These findings suggest that a prevention strategy addressing potentially modifiable risk factors for stillbirth (overweight and obesity, advanced maternal age, and smoking) in high-income countries may achieve substantial reductions in stillbirth rates.