Conflicts in the Last Fifty Years and Subsequent Effects on the Male: Female Ratio at Birth

Introduction: Male births occur slightly in excess of female births. In man, the ratio of male divided by total live births (M/F) is expected to approximate 0.515. Warfare has been shown to exert significant effects on M/F. This study was carried out in order to identify any such effects on M/F in belligerent countries in recent conflicts.
Methods: Births were obtained from a World Health Organisation Mortality database. Recent wars (post Second World War) were identified. Chi-square tests were used throughout. Male and female births in belligerent countries were compared to the aggregate of the previous and following years. Countries included were those with available data for periods spanning identified wars.
Results: This study analysed 260747284 live births. M/F in the United States increased significantly during the Korean (p=0.011) and Vietnam (p=0.011) conflicts but decreased during the Gulf War (p=0.02) and there were no changes during the invasion of Iraq. There was no significant shift in M/F in Greece during the invasion of Cyprus, in England and Argentina in the Falkland war and in the Balkans during the Yugoslavian wars. The South Ossetia and Abkhazia Wars were associated in rises in M/F in the Southern Caucasus (Armenia, Azerbaijan, Georgia) only after the wars, and then serially to the end of the 20th century (probably due to sex-selective terminations of pregnancy in favour of male births). The Portuguese Colonial War lowered Portugal’s M/F during the last year of conflict (1974, p=0.0001).
Discussion: This study confirms the observation that M/F rises during lengthy periods of warfare, and may fluctuate even during short periods of conflict. The former has been attributed to increased coital rates which increase conception rates early in the menstrual cycle, skewing M/F in favour of male conceptions. The latter may be due to the known M/F lowering effect of stress.