Environmental Public Health Tracking: Sex Ratio Data

Reproduction is complex, and many factors affect parents’ ability to make a baby, carry the baby to term, and deliver the baby without complications.  These factors include age, genetics, income/education level, and many others.

Sex ratio is one type of reproductive outcome.  Review the FAQs below for more information about sex ratio.

Access birth outcomes data

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What is sex ratio at birth?

The sex ratio at birth is the ratio of male to female births. The sex ratio is calculated as a ratio of total males/total females born in a geographic area (like in a certain state, county, zip code, census tract, or block group) at a certain time (one year or multiple years).

The worldwide expected sex ratio at birth (male to female) is 1.05. The sex ratio at birth is calculated as the number of male births divided by female births multiplied by 1,000.

(Number of male births/number of female births) X 1000 = Sex Ratio

This ratio has been found to be significant in evolution to ensure the population has the appropriate number of males and females of reproductive age to keep the population sustained.

What is the relationship between sex ratio and the environment?

Although the process which determines the sex of the infant is not completely understood, some have suggested that environmental hazards can affect how many males are born due to exposure to endocrine disrupting chemicals or contaminants impacting gene-expression. More research is needed about this relationship.

Where can I learn more about sex ratio?

Last Revised: April 2, 2020