DefinitionThe ratio of total males/total females born in a geographic area at a certain time.
NumeratorThe total number of full-term, singleton male infants born in a specified geographic area during and time period.
DenominatorThe total number of full-term, singleton female infants born in a specified geographic area during and time period.
Why Is This Important?Population growth is, in part, related to the number of live male children. Numerous studies have reported changes in the ratio of males to females at birth; many of the studies have found a reduction in male relative to female births in different countries throughout the world. Although the mechanism which determines the sex of the infant is not completely understood, some, but not all, have suggested that environmental hazards can affect how many males are born. Biological parent(s) and/or the fetus can come in contact with and become exposed to different hazards referred to as endocrine disruptors. Fewer males are conceived when exposure to endocrine disruptors results in a decrease in testosterone. Because states have accurate Vital Statistics (VS) records on the sex of live births, changes over time in the sex ratio of infants can be measured as the ratio of males to females.
Other ObjectivesCDC Environmental Public Health Tracking, Nationally Consistent Data and Measures (EPHT NCDM)