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Objective: In humans, male exceed female live births. This ratio is conventionally referred to (M/F) male to female ratio and is used to denote male divided by total births. This ratio is influenced by a large number of factors and has been shown to exhibit seasonality. This study was carried out in order to ascertain whether seasonal variation in M/F exists in United States and whether such variations are influenced by race. Material and Methods: Births by gender and by race for 2003-13 were obtained from CDC (Centers for Disease Control and Prevention) Wonder section as four races: White, Black/African American, Asian/Pacific Islander and American Indian/Alaska Native. Analysis of variance (ANOVA) and autoregressive integrated moving average (ARIMA) tests were carried out. Results: This study analysed 90 206 292 live births (M/F 0.51182) over 2003-13. M/F was highest in Asian/Pacific Islander (p < 0.0001), followed by White (p = 0.002), American Indian/Alaska Native (p = 0.04) and Black/African American. Significant seasonality was present overall, with a peak in June, for Whites more than Black/African American and absent in the test. Conclusion: Parental stress lowers M/F, and the lower M/F found in Black/African and American Indian/Alaskan births may be stress-related. The dampened seasonality noted in Black/African American births may also be due to this phenomenon. More males are born in spring, as in other species, with interesting inter-racial differences.

In humans, male births exceed female births. This ratio is conventionally expressed to M/F and is influenced by a large number of factors, including stress. This study was carried out in order to ascertain whether the known seasonal variation in M/F in the United States (peaking in June) is affected by the quadrennial elections (November), and whether any such influences vary by race.

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