Elevated risk of stillbirth in males : systematic review and meta-analysis of more than 30 million births

Background: Stillbirth rates have changed little over the last decade, and a high proportion of cases areunexplained. This meta-analysis examined whether there are inequalities in stillbirth risks according to sex. Methods: A systematic review of the literature was conducted, and data were obtained on more than 30 millionbirth outcomes reported in observational studies. The pooled relative risk of stillbirth was estimated usingrandom-effects models. Results: The crude mean rate (stillbirths/1,000 total births) was 6.23 for males and 5.74 for females. The pooledrelative risk was 1.10 (95% confidence interval (CI): 1.07–1.13). The attributable fraction in the whole population was4.2% (95% CI: 3.70–4.63), and the attributable fraction among male fetuses was 7.8% (95% CI: 7.0–8.66). Studypopulations from countries with known sex-biased sex selection issues had anomalous stillbirth sex ratios andhigher overall stillbirth risks than other countries, reflecting increased mortality among females. Conclusions: Risk of stillbirth in males is elevated by about 10%. The population-attributable risk is comparableto smoking and equates to approximately 100,000 stillbirths per year globally. The pattern is consistent acrosscountries of varying incomes. Given current difficulties in reducing stillbirth rates, work to understand the causes ofexcess male risk is warranted. We recommend that stillbirths are routinely recorded by sex. This will also assist inexposing prenatal sex selection as elevated or equal risks of stillbirth in females would be readily apparent andcould therefore be used to trigger investigation