title: The influence of migration on secular trends in sex ratios at birth in cuba in the past fifty years.
abstract: 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 Organisation 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Paediatrics, Mater Dei Hospital, Malta. victor.e.grech@gov.m.
authors.forename: V
authors.initials: V
authors.lastname: Grech