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Table 1 Total number of births and preterm births and prevalence of preterm birth (as a percentage) according to maternal characteristics and perinatal health behaviors in California from 2007 to 2016

From: Temporal trends, patterns, and predictors of preterm birth in California from 2007 to 2016, based on the obstetric estimate of gestational age

Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016
Number of births 554,689 546,201 524,058 508,124 500,367 502,124 492,921 500,404 490,383 487,818
Number of preterm births 50,108 48,796 45,394 42,909 42,080 41,839 40,885 40,767 40,947 41,555
Percentage of preterm births 9.0 8.9 8.7 8.4 8.4 8.3 8.3 8.2 8.4 8.5
Variable
Maternal age (years)
  < 20 9.1 8.8 8.4 8.2 8.2 8.1 8.0 8.0 8.0 8.3
 20–24 8.1 8.0 7.7 7.6 7.4 7.4 7.4 7.1 7.5 7.7
 25–29 8.2 8.1 7.8 7.6 7.6 7.6 7.6 7.3 7.5 7.7
 30–34 9.0 8.9 8.6 8.4 8.4 8.3 8.1 8.0 8.2 8.2
 35–39 10.7 10.6 10.4 10.0 10.0 9.7 9.7 9.5 9.7 9.9
 40–54 14.2 14.4 14.1 13.5 13.6 13.3 13.2 13.2 13.5 13.6
Maternal race and ethnicity
 Hispanic 8.6 8.4 8.2 8.0 8.1 8.1 8.2 8.2 8.4 8.7
 Whitea 9.0 8.8 8.5 8.2 8.0 7.6 7.7 7.3 7.5 7.6
 Asianb 8.8 8.8 8.8 8.3 8.4 8.3 8.0 7.5 7.8 8.1
 Pacific Islanderc 10.7 10.3 9.4 10.3 8.6 8.8 8.9 9.1 10.8 9.6
 African American 12.7 13.0 12.3 12.2 11.7 11.9 11.6 11.9 11.7 11.4
 Multiple race 9.8 9.1 9.2 9.1 8.6 9.1 8.7 9.0 8.9 9.3
 American Indiand 10.4 10.6 9.3 10.0 8.8 8.8 10.0 8.9 10.1 10.3
 Other/unknowne 12.8 13.0 11.7 12.2 12.0 11.3 11.1 11.6 10.9 10.5
Maternal education level
 Less than high school diploma 8.8 8.7 8.5 8.3 8.4 8.4 8.7 9.0 9.3 9.5
 High school diploma 8.9 9.0 8.5 8.4 8.4 8.2 8.2 8.1 8.3 8.6
 Some college or associate degree 9.4 9.1 8.8 8.8 8.7 8.5 8.5 8.3 8.5 8.6
 Bachelor’s degree or higher 8.9 8.7 8.5 8.0 7.9 7.9 7.6 7.3 7.5 7.6
 Unknown 10.9 11.3 10.6 10.5 10.4 10.2 10.5 10.2 9.8 10.0
Maternal nativity
 Foreign-born 8.2 8.2 8.0 7.8 8.0 7.9 7.9 7.8 8.1 8.4
 United States-born 9.7 9.5 9.1 8.9 8.7 8.6 8.5 8.3 8.5 8.6
Maternal demographic region
 Central Coast 8.1 8.1 7.7 7.7 7.7 7.4 7.8 7.4 7.9 7.9
 Greater Bay Area 8.5 8.6 8.6 8.4 8.1 8.4 8.2 7.9 8.1 8.3
 Inland Empire 9.5 9.0 8.9 8.6 8.4 8.7 8.5 8.3 8.5 8.8
 Los Angeles County 9.3 9.3 8.8 8.6 8.7 8.5 8.5 8.4 8.7 8.8
 Northern and Sierra 8.4 8.0 7.6 7.4 7.6 7.5 7.7 7.4 8.0 8.1
 Orange County 8.7 8.3 8.5 8.1 8.2 7.8 7.6 7.3 7.5 7.9
 Sacramento area 8.8 8.5 8.3 8.2 8.1 8.0 7.9 8.1 8.0 8.1
 San Diego area 9.5 9.0 9.0 8.4 8.4 8.3 8.1 8.2 8.0 8.4
 San Joaquin Valley 9.4 9.7 9.1 8.9 9.0 8.8 8.9 8.8 9.0 9.0
Source of prenatal care payment
 Private 9.2 9.0 8.8 8.7 8.5 8.4 8.2 8.1 8.2 8.3
 Medi-Cal 8.7 8.6 8.3 8.1 8.1 8.2 8.3 8.2 8.5 8.7
WIC Participation
 No 9.5 9.4 9.1 8.9 8.7 8.6 8.4 8.1 8.3 8.4
 Yes 8.6 8.5 8.3 8.0 8.2 8.1 8.2 8.2 8.4 8.6
First trimester prenatal care initiation
 No 9.1 8.6 8.3 8.3 8.2 8.2 8.2 8.1 8.2 8.5
 Yes 8.9 8.9 8.6 8.4 8.4 8.3 8.2 8.1 8.3 8.4
Parity
 Primiparous 8.4 8.2 8.0 7.8 7.7 7.7 7.7 7.4 7.7 7.8
 Multiparous (2–5) 9.3 9.2 8.9 8.7 8.6 8.5 8.4 8.4 8.5 8.7
 Multiparous (6–12) 14.9 15.2 15.0 14.6 13.9 14.6 14.7 15.3 15.3 15.6
Plurality
 Singleton births 8.0 7.9 7.5 7.4 7.3 7.3 7.2 7.1 7.3 7.5
 Multiple births 60.9 59.2 59.0 57.4 57.4 56.0 55.0 54.4 55.8 56.8
Maternal smoking during both first and second trimesters
 No 8.9 8.8 8.6 8.4 8.3 8.2 8.2 8.1 8.2 8.4
 Yes 15.7 15.0 14.6 14.2 14.8 15.6 16.4 15.5 16.9 17.9
Prepregnancy body mass index (kg/m2)
 Underweight (≤18.5) 9.7 10.0 9.4 9.0 8.9 8.8 8.6 8.5 8.4 8.7
 Normal (18.5–24.9) 8.5 8.4 8.1 7.9 7.9 7.7 7.7 7.4 7.5 7.7
 Overweight (25.0–29.9) 8.8 8.5 8.3 8.1 8.3 8.2 8.1 8.1 8.2 8.6
 Obese I (30.0–34.9) 9.6 9.3 9.1 9.0 8.9 8.8 8.9 9.0 9.3 9.3
 Obese II (35.0–39.9) 10.1 10.1 10.4 9.4 9.1 10.1 9.4 9.6 10.1 10.1
 Obese III (≥ 40) 10.8 11.2 10.0 11.2 10.3 10.1 10.4 10.0 10.6 10.4
  1. All live births were delivered at 17–47 completed weeks of gestation based on obstetric estimates and birthweight of ≥500 g at birth. Births with missing information on gestational age or birthweight were excluded
  2. Total number of births = 5,107,089
  3. Race/ethnicity results were tabulated using the following race/ethnic groups: Hispanic, White, Asian/ Pacific Islander, African American, Multiple race (two or more races), American Indian, and other
  4. Hispanic origin was determined first and could include any race group. Next, members of the two or more races group were identified and are not reported in the single-race groups. To remain consistent with the population data obtained from the California Department of Finance, the single-race groups are defined as follows:
  5. a“White” race group includes White women
  6. b“Asian” race group includes Asian Indian, Asian (specified/unspecified), Cambodian, Chinese, Filipino, Hmong, Japanese, Korean, Laotian, Thai, and Vietnamese women
  7. c“Pacific Islander” race group includes Guamanian, Hawaiian, Samoan, and other Pacific Islander women
  8. d“American Indian” race group includes Aleutian, American Indians, and Eskimo women
  9. e“Other/unknown” includes not stated or unknown
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