ABSTRACT

Objective: In humans, males’ births exceed females’ births. This ratio is conventionally referred to as M/F and is used to denote male births 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 the United States of America and whether such variations are influenced by race.

Materials and Methods: Data on births by gender and race from 2003 to 2013 were obtained from Centres for Disease Control and Prevention Wonder section as four races: White, Black/African American, Asian/Pacific Islander and American Indian/Alaska Native. ANOVA and ARIMA tests were carried out.

Results: This study analysed 45 103 146 live births (M/F 0.51182) over 2003 to 2013. 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.

Conclusion: Parental stress lowers M/F, and 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 were born in spring, as in other species, with interesting inter-racial differences.