BACKGROUND:

Human sex ratio at birth differs from one population to the other. This variation has been attributed to cultural practices, seasonal variation, small-family size policy and sex selective technology. Information on secondary sex ratio in Nigeria is limited.

AIMS AND OBJECTIVE:

To analyzed human sex ratio at birth for samples of the Nigerian population in 4 urban settings in Southwest Nigeria, in order to know the trend and to compare the findings with those of previous reports.

MATERIALS AND METHODS:

Data were collected from Obafemi Awolowo University (OAU) teaching hospital at Ile Ife and Wesley Guild hospital at Ilesa, Osun state; General hospital at Ogbomoso, Oyo state and Ekiti state specialist hospital at Ado-Ekiti, Ekiti state. The data consisted of 35 209 live single births recorded between 1995 and 2004. Each set of data was analyzed to determine the sex ratio by year, month and quarterly values. Chi-square analysis was used to determine the deviation of the sex ratios for the years from the average value.

RESULTS:

The annual average ratios of 104.7:100, 102.8:100, 98.9:100 and 100.8:100 were recorded for OAU teaching hospital, Wesley Guild Hospital, General Hospital and Ekiti State specialist hospital, respectively. When pooled together, the average ratio was 102.7:100. This shows some bias for male births. Data also indicates more male birth in the rainy season, suggesting a seasonal variation of sex ratio.

CONCLUSION:

These findings are representative of the populations in southwest Nigeria and are comparable to values obtained for other regions in Nigeria and other populations of African origin.