Significantly Increased Risk of Stillbirth in Males

A new large-scale study demonstrates that the risk of stillbirth is about ten percent higher in boys, equating to a loss of around 100,000 additional male babies per year.

Researchers at the University of Exeter (United Kingdom) and the University of Salford (United Kingdom) conducted a systematic review of literature, obtaining data on more than 30 million birth outcomes as reported in observational studies. The pooled relative risk of stillbirth was estimated using random-effects models. The results showed that the crude mean rate of stillbirths was 6.23 per 1,000 for males and 5.74 for females; the pooled relative risk was 1.10.

The study also found that the percentage of increased risk of mortality in males was consistent across both high- and low-income countries. The only exceptions to this global pattern were found in reports from China and India, where sex-biased induced abortion is a known issue; the data in these countries showed equal ratios of stillbirth in males and females, and higher overall stillbirth risks than other countries. The mortality rates among females in these studies were 1.7 times the expected levels. The study was published on November 27, 2014, in BMC Medicine.

“Stillbirth is a common occurrence, even in rich countries with good healthcare systems: every day, eleven babies are stillborn in the UK. Uncovering why male babies are at higher risk could be a first step towards developing new approaches to prevention, including sex-specific management of high-risk pregnancies,” said lead author Fiona Mathews, PhD, of the University of Exeter. “The routine recording of stillbirth type by fetal sex would help uncover which types of stillbirth are sex-linked. In countries showing reversed patterns of stillbirth risk, work is warranted to clarify whether female feticide or other explanations can account for the elevated risks to females.”

Differences in male and female development begin early in life. In animal models, male embryos have faster development and higher metabolic rates than females, potentially leaving the male fetus more vulnerable to a range of stressors, including endocrine fluctuations, oxidative stress, and nutritional compromise. Environmental factors experienced by the mother, including obesity, smoking, advanced maternal age, and social deprivation also affect the male embryo more than the female.

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University of Exeter
University of Salford