Stillbirths in High-Income Countries: Lifestyle, Environmental and Sociodemographic Risk Factors

Background Stillbirth rates in high-income countries have shown little improvement over the last decade. However, many lifestyle, sociodemographic and environmental factors are modifiable, and may help reduce stillbirth rates. Systematic review, meta-analysis and cohort studies identifying lifestyle, sociodemographic and environmental factors are powerful methods for guiding stillbirth prevention in high-income countries. Better understanding of potentially modifiable risk factors of stillbirth at a global level as well as a local level will enable more effective prevention of stillbirth. Aims 1. To systematically review case-control and cohort studies to identify lifestyle, environmental and sociodemographic risk factors, and their association with stillbirth within high-income countries. 2. To use data contained with the perinatal dataset of South Australia (SA) to identify lifestyle, environmental and sociodemographic risk factors of stillbirth relevant to the Australian population. 3. To inform and recommend individual, local community, national policy, and practice changes to prevent stillbirths. Methods To following methods were employed to address the identified aims of this research; 1. Systematic review of cohort and case-control studies published between 1998-2020 examining factors of interest associated with stillbirth were identified through database searches. The primary outcome of interest, stillbirth, is defined as a birth with no signs of life ≥20 weeks gestational age (GA) or ≥400 grams birthweight. Adjusted odds ratios were calculated through random effects meta-analysis for individual risk factors and stratified by GA where possible. 2. All births registered in the SA routine data collection over the period of 1998-2016 were included in a cohort study of stillbirth risk in SA. Associations between stillbirth risk and lifestyle, environmental and social determinant factors were explored, using multivariable logistic regression. Population Attributable Fractions (PAF) were calculated for factors demonstrating the strongest associations with stillbirth in SA. Results 1. The systematic review and meta-analysis included 390 studies assessing relevant risk factors of stillbirth in high-income countries. Strongest associations with stillbirth were seen for inadequate or no antenatal care, maternal assault during pregnancy, supine sleep position, maternal age ≥45 years, maternal body mass index ≥40, and pre-existing diabetes. Other factors showing an increase in stillbirth risk were; unmarried status, low household income, advanced paternal age, pre-existing hypertension, nulliparity or ≥3 previous births, small or large interpregnancy interval, drug, alcohol, caffeine or cigarette use, unplanned place of birth, parental occupation, maternal ethnicity or country of birth, high exposure to tap water pollution, public or uninsured insurance status and remote/regional living. Maternal university education, H1N1 vaccination, and residential segregation, showed preventative associations with stillbirth odds. 2. From the SA perinatal database, a total of 363,959 births were included in a large cohort study investigating stillbirth risk factors. An inadequate number of antenatal visits was associated with the strongest odds of stillbirth. Other factors found to have important associations with stillbirth odds were: pregnant plant or machine operators, maternal age ≥40 years, paternal pensioners, South Asian country of birth and Aboriginal/Torres Strait Islander women. Odds of stillbirth were increased in regional and remote areas in association with inadequate antenatal care visits, maternal age 35-40 years, Aboriginal and/or Torres Strait Islander women, paternal occupations; tradesperson or unemployed. Discussion and conclusion Comprehensive systematic review and detailed SA cohort data have identified risk factors that potential actions and strategies can target to prevent stillbirth and to decrease rates within high-income countries. Although there is a lack of global consensus on definitions of stillbirth, it is clear that the identified risk factors need to be addressed at local and national policy levels. Risk factors found to have the largest impact on stillbirth odds such as maternal assault, inadequate antenatal care, supine sleep position, and occupation are all factors that may be modified to mitigate the risk of stillbirth. Knowledge of these preventive factors will help families to decrease their risk of stillbirth and to also address and reduce inequity.Thesis (Ph.D.) -- University of Adelaide, Adelaide Medical School, 202