Reduced Male:Female Ratio at Birth in Small Islands.

Background The male:female ratio at birth (M/F: male births divided by total births) is anticipated to approximate 0.515. The M/F in Micronesia in the Pacific Ocean has been noted to be higher than anticipated. This study analysed M/F in island populations available from a World Health Organization dataset. Methods The following islands were identified from the dataset as being sufficiently complete for analysis: Bahamas, Barbados, Puerto Rico, Trinidad and Tobago, and Mauritius. Results There were 540 8629 live births available for analysis over the period 1960-2009 with an overall M/F of 0.5106 (95% CL 0.5101, 0.5110). There were no secular trends in M/F. Conclusion The M/F in these equatorial islands is lower than anticipated, and the reason for this is unknown.