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. Methods: Annual national data for male and female live births in Cuba with contingency tables were obtained from the World Health Organization and analysed. Results: There were 3 736 718 male and 3 534 270 female births (1960-96). Births declined steadily over the entire period. The male-female ratio at birth remained relatively stable over the period 1960- 1985 with significant sharp dips for the years 1966, 1980 and 1985. There was a sharp rise in M/F from 1966 to 1969, another rise after 1985, a steep drop to 1989, and then a sharp rise once more after 1993 (all p < 0.0001). Conclusion: The single year dips are associated with the passage of laws in the United States of America (USA) that facilitated Cuban entry to the USA. The increases in M/F tended to be associated with a skew toward an efflux from Cuba that was predominantly male. This paralleled the situation in the Second World War where a surplus of women left behind led to an increase in M/F in belligerent countries. To the author's knowledge, this is the first report of migration influencing M/F.

Life change events Sex ratio Cuba Birth rate

male Birth Rate female live birth world health organization Cuba contingency table United States sex ratio human adult life event war