Table 1.
Descriptive characteristics (percentages)a of preterm case and term control infants, California, 1998–2011 (n=225,374)
| Characteristic | Gestational age in weeks at delivery | ||||
|---|---|---|---|---|---|
|
| |||||
| CASES | CONTROLS | ||||
|
| |||||
| 20–23 n=515 |
24–27 n=1,792 |
28–31 n=3,098 |
32–36 n=22,508 |
37–41 n=197,261 |
|
| Maternal age (years) | |||||
| <20 | 19.2 | 19.4 | 20.1 | 16.2 | 14.2 |
| 20–24 | 24.7 | 27.2 | 28.3 | 28.8 | 29.9 |
| 25–29 | 23.1 | 23.8 | 23.2 | 25.7 | 28.0 |
| 30–34 | 18.8 | 17.4 | 16.3 | 18.2 | 18.4 |
| >35 | 14.2 | 12.2 | 12.1 | 11.1 | 9.5 |
| Missing | 0 | 0 | 0.1 | <0.1 | <0.1 |
| Maternal race/ethnicity | |||||
| White, nonHispanic | 19.8 | 22.7 | 24.1 | 28.4 | 29.4 |
| White, Hispanic | 60.6 | 57.1 | 54.9 | 54.8 | 57.0 |
| Black | 9.5 | 9.4 | 9.6 | 6.3 | 4.5 |
| Asian | 7.0 | 8.7 | 8.8 | 8.3 | 7.1 |
| Other | 1.9 | 1.6 | 1.9 | 1.8 | 1.5 |
| Missing | 1.2 | 0.4 | 0.6 | 0.6 | 0.6 |
| Maternal education | |||||
| Less than high school | 36.9 | 34.0 | 37.1 | 33.7 | 32.6 |
| High school | 32.8 | 34.2 | 33.8 | 31.0 | 31.8 |
| More than high school | 27.8 | 29.4 | 26.8 | 33.6 | 34.0 |
| Missing | 2.5 | 2.5 | 2.3 | 1.8 | 1.6 |
| Prenatal care initiation by fifth month of gestation | |||||
| Yes | 85.2 | 88.2 | 85.9 | 88.4 | 91.8 |
| No | 8.9 | 7.2 | 10.3 | 8.6 | 6.4 |
| Missing | 5.8 | 4.6 | 3.8 | 3.0 | 1.8 |
| Parity | |||||
| 1 | 41.8 | 45.1 | 38.1 | 35.8 | 34.8 |
| ≥2 | 57.9 | 54.9 | 61.8 | 64.1 | 65.2 |
| Missing | 0.4 | <0.1 | 0.2 | <0.1 | 0.1 |
| Payer type for delivery | |||||
| Medi-Cal | 63.5 | 61.9 | 63.7 | 60.0 | 56.9 |
| Private | 28.9 | 30.5 | 30.2 | 35.5 | 39.7 |
| Uninsured | 6.2 | 6.2 | 4.5 | 2.9 | 1.7 |
| Other | 1.0 | 1.0 | 1.2 | 1.3 | 1.5 |
| Missing | 0.4 | 0.4 | 0.4 | 0.3 | 0.2 |
| Infant sex | |||||
| Male | 56.5 | 57.1 | 58.5 | 55.1 | 50.6 |
| Female | 43.5 | 42.8 | 41.5 | 44.9 | 49.4 |
| Missing | 0 | <0.1 | 0 | <0.1 | <0.1 |
| Infant Birth Year | |||||
| 1998 | 5.8 | 5.7 | 6.3 | 4.9 | 6.7 |
| 1999 | 6.4 | 5.5 | 6.3 | 4.7 | 6.7 |
| 2000 | 7.4 | 6.8 | 6.4 | 5.1 | 6.9 |
| 2001 | 5.6 | 6.3 | 7.0 | 5.7 | 6.9 |
| 2002 | 5.6 | 5.7 | 6.6 | 5.9 | 7.1 |
| 2003 | 5.1 | 5.9 | 6.3 | 6.2 | 7.4 |
| 2004 | 9.5 | 6.9 | 6.9 | 6.4 | 7.9 |
| 2005 | 8.7 | 7.5 | 9.0 | 6.9 | 9.1 |
| 2006 | 8.0 | 7.9 | 8.4 | 7.7 | 9.5 |
| 2007 | 8.0 | 8.5 | 8.8 | 9.4 | 6.8 |
| 2008 | 5.4 | 8.8 | 7.6 | 10.0 | 6.7 |
| 2009 | 8.4 | 7.8 | 7.1 | 9.1 | 6.3 |
| 2010 | 7.4 | 7.6 | 6.5 | 9.0 | 6.1 |
| 2011 | 8.7 | 9.2 | 7.0 | 9.1 | 6.0 |
| Years 2007–2011 | 195 | 751 | 1141 | 10452 | 63021 |
| Prepregnancy body mass index (kg/m2) (2007–2011) | |||||
| Underweight (BMI<18.5) | 2.1 | 5.5 | 5.0 | 4.7 | 3.1 |
| Normal (18.5≤BMI<25) | 30.3 | 30.8 | 38.9 | 42.6 | 40.2 |
| Overweight (25≤BMI<30) | 19.5 | 26.1 | 22.8 | 23.0 | 24.7 |
| Obese (BMI≥30) | 27.2 | 24.1 | 20.0 | 18.0 | 20.3 |
| Missing | 21.0 | 13.6 | 13.3 | 11.8 | 11.8 |
| Poverty (2007–2011)b | |||||
| ≤107.25 | 20.5 | 16.1 | 16.5 | 17.5 | 19.4 |
| 107.26 – ≤180.14 | 13.3 | 17.7 | 17.3 | 18.2 | 19.4 |
| 180.15 – ≤260.29 | 20.0 | 19.4 | 18.6 | 19.0 | 19.5 |
| 260.30 – ≤365.66 | 21.0 | 21.0 | 22.4 | 20.8 | 19.6 |
| >365.66 | 21.5 | 23.0 | 22.4 | 21.6 | 19.3 |
| Missing | 3.6 | 2.7 | 3.0 | 2.9 | 2.7 |
a
Percentages may not equal 100 owing to rounding
b
Quintile cutoffs were determined among term births. The highest quintile reflects the highest degree of poverty.