Changing sex ratio in the United States, 1969-1995.
OBJECTIVE
To determine if the sex ratio of live births in the United States has changed during the 27 years from 1969 through 1995.


METHODS
Regression analysis of secular trends in sex ratios.


METHODS
Population-based data.


METHODS
Liveborn infants in the United States 1969-1995.


METHODS
Sex of liveborn infant.


RESULTS
The sex ratio (number of male births divided by number of female births) declined significantly among whites during the 27 years under study. Among black newborns, the sex ratio significantly increased during the same time period.


CONCLUSIONS
These secular trends could not be explained by changing maternal or paternal age, or by changing proportions of specific birth orders. Possible explanations for the observed changes in sex ratio include random fluctuations in sex ratio over time, changes in demographic characteristics of the population (other than the characteristics controlled for in this analysis), and changes in frequency or timing of intercourse. Environmental exposures are unlikely to account for the observed trends.
National Center for Environmental Health, Centers for Disease Control and Prevention, Chamblee, Georgia 30341, USA. yzm1@cdc.gov
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Marcus
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Kiely
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Xu
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McGeehin
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Jackson
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Sinks
D044383:Black People; D005260:Female; D006306:Health Surveys; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D016017:Odds Ratio; D012044:Regression Analysis; D012744:Sex Ratio; D014481:United States; D044465:White People; D001741:Black or African American