The influence of the Chinese zodiac on the male-to-female ratio at birth in Hong Kong.

BACKGROUND Secular trends have been found in the male-female ratio at birth (M/F: male births divided by total births) in various countries, and this ratio is anticipated to approximate 0.515. Births in Dragon years are considered auspicious. Fertility is known to have increased in Dragon years in Hong Kong. This study analyzed M/F with reference to Dragon years. METHODS Annual national data for male and female live births in Hong Kong were obtained from the World Health Organization and analyzed with contingency Tables. RESULTS There were 3,827,347 live births (1960-2009). Births declined steadily, then increased from 2004 in association with M/F. M/F was stable prior to this time, with spikes in 1975-1976, 1988, and 2000, associated with increases in births for these same years. CONCLUSION M/F follows a U-shaped regression on cycle day of insemination. Families attempting to conceive children during Dragon years may have increased coital rates, inadvertently skewing M/F in favor of a male excess.