Regional differences in the sex ratio at birth in Mexico

OBJECTIVE: The sex ratio at birth, defined as males/total (M/T) approximates 0.515 but is affected by many factors. Acute and chronic stress have been shown to lower M/T, and both regional and racial differences exist. This study analysed regional differences in M/T in Mexico. MATERIAL AND METHODS: Live births by sex and year were available for 1994-2020. Regional births were available for 2010-2020 for five regions: North, Centre, West, East and South. RESULTS: There were 68,423,415 births for 1994-2020 and 25,436,687 for 2010-2020 (M/T=0.5060, 95% confidence interval: 0.5058-0.5062). M/T was <0.515 (p<0.0001). Live births correlated negatively with year (p<0.0001). M/T fell for 1994-2003 then rose to 2020 (p<0.0001). M/T was highest in North followed by West, South, Centre and East (p<0.0001). CONCLUSION: Chronic stress with socioeconomic deprivation may reduce M/T and may explain the low M/T found in this study from Mexico.