Major Risk Factors for Stillbirth in High-Income Countries: A Systematic Review and Meta-Analysis
Obstetrical and Gynecological Survey
Stillbirth rates in high-income countries have shown little or no improvement over the past two decades. Prevention strategies that target risk factors could be important in rate reduction. This systematic review and metaanalysis was done to identify priority areas for stillbirth prevention relevant to those countries. Methods Population-based studies addressing risk factors for stillbirth were identifi ed through database searches. The factors most frequently reported were identifi ed and
... dentifi ed and selected according to whether they could potentially be reduced through lifestyle or medical intervention. The numbers attributable to modifi able risk factors were calculated from data relating to the fi ve high-income countries with the highest numbers of stillbirths and where all the data required for analysis were available. Odds ratios were calculated for selected risk factors, from which population-attributable risk (PAR) values were calculated. Findings Of 6963 studies initially identifi ed, 96 population-based studies were included. Maternal overweight and obesity (body-mass index >25 kg/m²) was the highest ranking modifi able risk factor, with PARs of 8-18% across the fi ve countries and contributing to around 8000 stillbirths (≥22 weeks' gestation) annually across all high-income countries. Advanced maternal age (>35 years) and maternal smoking yielded PARs of 7-11% and 4-7%, respectively, and each year contribute to more than 4200 and 2800 stillbirths, respectively, across all high-income countries. In disadvantaged populations maternal smoking could contribute to 20% of stillbirths. Primiparity contributes to around 15% of stillbirths. Of the pregnancy disorders, small size for gestational age and abruption are the highest PARs (23% and 15%, respectively), which highlights the notable role of placental pathology in stillbirth. Pre-existing diabetes and hypertension remain important contributors to stillbirth in such countries. Interpretation The raising of awareness and implementation of eff ective interventions for modifi able risk factors, such as overweight, obesity, maternal age, and smoking, are priorities for stillbirth prevention in highincome countries. Panel: Search strategy and selection criteria We searched Medline (PubMed and Ovid), CINAHL, and the Cochrane Database of Systematic Reviews for reports published between the years 1998-2009, using a sensitive methodological fi lter for aetiology studies. Search terms were "stillb*", "fetal death", "fetal mortality", and "pregnancy outcome*". We excluded reports not published in English, animal studies, and studies from low-income and middle-income countries. Bibliographies of relevant retrieved studies and recent reviews were hand-searched for additional publications. Where recent data on specifi c factors were missing, we searched back to 1990-this extended search was done for studies on education, indigenous status, primiparity, and hypertension.