Associations of maternal age- and parity-related factors with trends in low-birthweight rates: United States, 1980 through 2000.
OBJECTIVE
We assessed the effects of changes in the maternal age-parity distribution and age-and parity-specific low-birthweight rates on low-birthweight trends in the United States.


METHODS
We used natality file data from 1980 through 2000 to assess very-low-birthweight and low-birthweight rates among singleton live-born infants.


RESULTS
Changes in age-and parity-specific low-birthweight rates were the main contributor to the overall trend in rates. However, changes in the age-parity distribution, primarily delayed childbearing, had a smaller but noticeable impact. The very-low-birthweight rate increased 27% among Black women, and changes in the age-parity distribution were associated with, on average, more than 20% of the increased rate during the 1990s. Among Hispanic and non-Hispanic White women, on average, more than 10% of the rate increase observed during the 1990s was associated with changes in the age-parity distribution.


CONCLUSIONS
Assuming minimal changes in age-specific rates, delayed childbearing may play an increasingly important role in low-birthweight trends in the United States.
Division of Birth Defects and Developmental Disabilities, National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, 1600 Clifton Rd, Mail Stop E-86, Atlanta, GA 30333, USA. qay0@cdc.gov
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D000293:Adolescent; D000328:Adult; D044383:Black People; D005260:Female; D006630:Hispanic or Latino; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D008423:Maternal Age; D008875:Middle Aged; D010298:Parity; D011159:Population Surveillance; D011247:Pregnancy; D014481:United States / Q000453:epidemiology; D044465:White People; D001741:Black or African American