Sex ratio


The ratio of male to female births

The expected sex ratio in the United States is 1.05, or 105 boys born for every 100 girls. A sex ratio above 1 means there are more males than females, while a sex ratio below 1 means there are more females than males. That means that the chance of a baby boy is about 51 percent, rather than 50/50.

Ratio of male to female births in Minnesota

 
 
Per 1,000 live births. Source: Minnesota Center for Health Statistics. National birth data is not yet available for 2016.

A lower sex ratio (closer to 1 rather than the expected 1.05) indicates that there are less male births than expected and may indicate environmental factors. The sex ratio in Minnesota has been consistently near 1.05, with some variation from year to year. In 2016, the sex ratio was 1.04 (1,044 males per 1,000 females). 


Sex ratio in Minnesota by mother's race/ethnicity

 
 
Per 1,000 live births. Categories are non-Hispanic ethnicity unless noted. Data are for 2012-2016. Source: Minnesota Center for Health Statistics. 

A lower sex ratio (closer to 1 rather than the expected 1.05) indicates that there are less male births than expected and may indicate environmental factors. The sex ratio varies only slightly by mothers’ race/ethnicity. However, the sex ratio is significantly lower for Asian or Pacific Islander mothers and for American Indian mothers, compared to the sex ratio for all races/ethnicities combined. This means that the ratio of male to female births is significantly lower than the expected 1.05 sex ratio for these races.


Sex ratio in Minnesota by mother's age

 
 
Per 1,000 live births. Data are for 2012-2016. Source: Minnesota Center for Health Statistics.

A lower sex ratio (closer to 1 rather than the expected 1.05) indicates that there are less male births than expected and may indicate environmental factors. Mothers in their 40s or older have a significantly higher ratio of male to female births than all ages combined, while teen mothers and mothers in their 30s had a lower sex ratio.

Environmental factors may influence sex ratio

Environmental factors such as exposure to chemicals that disrupt the endocrine system also may result in fewer male births, lowering the sex ratio. Endocrine disrupting chemicals are a group of synthetic and natural chemicals that may alter or affect the endocrine system in animals and possibly humans.

Plastic additives like phthalates and bisphenol A (BPA) are two of a number of chemicals that have been implicated as endocrine disrupting chemicals. However, the environmental factors that may influence sex ratio are not well understood, and additional research is needed to understand their effects on human health.