Columbia subject headings:
Pregnancy--Complications--United States--Statistics.
Pregnancy--Statistics.
United States--Statistics, Medical.
Harvard subject headings:
Childbirth--United States--Statistics.
Collaborative Perinatal Project (U.S.)
Pregnancy--Complications--United States--Statistics.
Pregnancy--United States--Statistics.
United States--Statistics, Medical.
Princeton subject headings:
Childbirth--United States--Statistics.
Collaborative Perinatal Project (U.S.)
Pregnancy--Complications--United States--Statistics.
Pregnancy--United States--Statistics.
Statistics.
United States--Statistics, Medical.