Columbia subject headings:
Birth order--America--Statistics.
Birth order.
Birth weight--America--Statistics.
Birth weight.
Infants--Mortality--America.
Infants--Mortality.
Maternal age--America--Statistics.
Maternal age.
Harvard subject headings:
Birth order--America--Statistics.
Birth order.
Birth weight--America--Statistics.
Birth weight.
Infants--America--Mortality.
Infants--Mortality
Infants--Mortality--America.
Maternal age--America--Statistics.
Maternal age.
Princeton subject headings: