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Table 1 Characteristics of singleton births in study sample compared with overall population of singleton births at 37-44 weeks of gestational age, California (1996-2006).

From: Ambient air pollution exposure and full-term birth weight in California

  Total Eligible Singleton Births
(n = 4,776,090)
Study Sample
(n = 3,545,177)
low birth weight (<2,500 grams) 2.3% 2.3%
maternal age (years)   
9 to 14 0.1% 0.2%
15 to 19 9.9% 10.2%
20 to 34 74.2% 74.3%
35 to 49 15.8% 15.4%
educational attainment   
none to 11th grade 30.2% 31.5%
12th grade 27.6% 27.6%
1-3 years college 19.8% 19.4%
4+ years college 22.4% 21.4%
marital status   
married 42.8% 42.0%
not married 22.5% 23.7%
not on form 27.9% 27.4%
missing 6.8% 6.9%
maternal race/ethnicity   
Hispanic 49.6% 51.5%
Black (non-Hispanic) 5.8% 6.3%
American Indian/Alaska Native (non-Hispanic) 0.4% 0.3%
Asian Pacific Islander (non-Hispanic) 11.9% 12.0%
Other Race (non-Hispanic) 0.0% 0.0%
White (non-Hispanic) 32.2% 29.6%
missing 0.1% 0.1%
maternal birthplace   
Mexico 27.6% 28.6%
other or unknown foreign country 18.5% 19.2%
US and her territories 53.8% 52.1%
missing 0.1% 0.1%
parity   
first live birth 39.5% 39.7%
maternal risk factors   
anemia, diabetes, hypertension and/or herpes 4.5% 4.4%
none of the above 86.1% 86.4%
missing 9.4% 9.2%
Kotelchuk index   
no prenatal care 1.6% 1.8%
inadequate 9.0% 9.0%
intermediate 11.8% 11.7%
adequate 44.1% 43.8%
more than adequate 33.5% 33.7%
insufficient information 0.1% 0.1%
  1. Eligible singleton births include singleton births with a gestational age of 37-44 weeks and information for birth weight, sex, date of birth, maternal educational attainment, parity, and a maternal age of 9 to 49 years old. Study sample includes eligible singleton births within 10 km of an air monitor active throughout pregnancy.