Major risk factors for stillbirth in high-income countries: a systematic review and meta-analysis

Summary

Background

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 meta-analysis was done to identify priority areas for stillbirth prevention relevant to those countries.

Methods

Population-based studies addressing risk factors for stillbirth were identified through database searches. The factors most frequently reported were identified and selected according to whether they could potentially be reduced through lifestyle or medical intervention. The numbers attributable to modifiable risk factors were calculated from data relating to the five 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 identified, 96 population-based studies were included. Maternal overweight and obesity (body-mass index >25 kg/m²) was the highest ranking modifiable risk factor, with PARs of 8–18% across the five 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 effective interventions for modifiable risk factors, such as overweight, obesity, maternal age, and smoking, are priorities for stillbirth prevention in high-income countries.

Funding

The Stillbirth Foundation Australia, the Department of Health and Ageing, Canberra, Australia, and the Mater Foundation, Brisbane, Australia.

Introduction

In high-income countries, one in every 200 pregnant women reaching 22 weeks' gestation will have a stillborn baby.¹ Although notable reductions in stillbirth rates in such countries have been achieved since the 1940s, rates have become stable or decreased only marginally in many regions over the past decade. Most stillbirths are now antepartum deaths, frequently associated with placental dysfunction and growth restriction,¹ and many remain unexplained.²

Risk factors for stillbirth are increasingly being investigated and reported. Identification of priorities for prevention from individual published studies, however, is problematic. We undertook a systematic review of studies relevant to present practice to clearly identify important risk factors for stillbirth in high-income countries. If some of these risk factors can be avoided or prevented, fewer parents will experience the intense grief and lasting psychosocial trauma of stillbirth.³