Table 1.
Distribution of covariates by gestational age in births in the four most populous counties in San Joaquin Valley, California, 2000–2006 (%) (N=263,204).
| Covariate | Gestational age in weeks (%)a | Total | |||||
|---|---|---|---|---|---|---|---|
| 37–42 n=232,241 |
34–36 n=22,321 |
32–33 n=4011 |
28–31 n=2938 |
24–27 n=1233 |
20–23 n=460 |
||
| First born | 35.2 | 32.9 | 33.9 | 34.7 | 38.5 | 34.1 | 35.0 |
| Neighborhood low SES | 17.5 | 20.6 | 24.1 | 23.9 | 23.8 | 27.4 | 17.9 |
| Medi-Cal payment of costs | 53.7 | 60.8 | 65.0 | 65.8 | 63.3 | 70.9 | 54.7 |
| Male | 50.9 | 54.0 | 54.4 | 55.3 | 56.4 | 57.8 | 51.3 |
| Cesarean section | 24.8 | 28.4 | 34.6 | 41.1 | 41.0 | 30.0 | 25.5 |
| Prenatal care in 1st trimester | 81.7 | 77.7 | 73.6 | 68.8 | 70.2 | 66.5 | 81.0 |
| Maternal age (years) | |||||||
| <20 | 13.3 | 15.3 | 16.9 | 20.1 | 18.7 | 21.1 | 13.7 |
| 20–24 | 28.8 | 28.5 | 28.3 | 28.3 | 27.2 | 29.8 | 28.8 |
| 25–29 | 27.6 | 25.3 | 23.4 | 22.8 | 22.6 | 21.3 | 27.2 |
| 30–34 | 19.4 | 18.3 | 18.0 | 15.7 | 18.5 | 16.5 | 19.2 |
| ≥35 | 10.9 | 12.6 | 13.5 | 13.1 | 13.1 | 11.3 | 11.1 |
| Race/ethnicity | |||||||
| White, non-Hispanic | 30.3 | 25.6 | 22.6 | 22.8 | 22.4 | 19.1 | 29.6 |
| Asian | 7.5 | 8.8 | 8.8 | 9.9 | 9.3 | 8.5 | 7.7 |
| African-American | 4.9 | 6.7 | 7.9 | 9.2 | 9.0 | 8.0 | 5.1 |
| Hispanic | 55.8 | 57.4 | 59.3 | 56.6 | 57.7 | 61.3 | 56.0 |
| Other | 1.5 | 1.5 | 1.5 | 1.5 | 1.6 | 3.0 | 1.5 |
| Year | |||||||
| 2000 | 13.2 | 12.4 | 12.4 | 12.3 | 13.7 | 11.3 | 13.1 |
| 2001 | 13.4 | 12.6 | 11.5 | 12.3 | 11.0 | 8.0 | 13.2 |
| 2002 | 13.7 | 12.9 | 13.1 | 11.7 | 10.9 | 9.8 | 13.6 |
| 2003 | 13.9 | 13.9 | 13.8 | 12.5 | 11.6 | 9.8 | 13.9 |
| 2004 | 14.5 | 14.6 | 14.2 | 13.0 | 13.1 | 12.2 | 14.4 |
| 2005 | 15.1 | 16.1 | 15.7 | 18.7 | 21.1 | 26.5 | 15.2 |
| 2006 | 16.3 | 17.5 | 19.2 | 19.7 | 18.7 | 22.4 | 16.5 |
| Education | |||||||
| <High school | 11.8 | 12.2 | 13.5 | 11.7 | 11.4 | 13.9 | 11.9 |
| High school | 52.0 | 56.1 | 57.5 | 61.1 | 58.5 | 61.5 | 52.6 |
| Some college | 21.0 | 19.2 | 17.9 | 16.9 | 18.9 | 15.0 | 20.7 |
| College degree | 12.9 | 9.7 | 7.9 | 7.0 | 7.3 | 7.0 | 12.5 |
| Missing | 2.3 | 2.8 | 3.1 | 3.4 | 3.9 | 2.6 | 2.3 |
| County | |||||||
| Fresno | 32.5 | 35.2 | 35.9 | 37.4 | 44.3 | 53.5 | 32.9 |
| Stanislaus | 18.5 | 16.7 | 16.5 | 17.1 | 14.7 | 12.2 | 18.3 |
| Kern | 23.8 | 25.5 | 27.0 | 24.2 | 21.3 | 19.4 | 23.9 |
| San Joaquin | 25.3 | 22.6 | 20.7 | 21.3 | 19.8 | 15.0 | 24.9 |
| Pregnancy complications | |||||||
| Diabetes | 2.0 | 2.7 | 2.4 | 1.6 | 1.2 | 0.7 | 2.0 |
| Hypertension | 1.5 | 3.4 | 5.1 | 4.9 | 3.6 | 1.1 | 1.7 |
| Mean (SD) | |||||||
| Infant birth weight (g) | 3426 (466) | 3003 (582) | 2663 (761) | 2289 (976) | 1818 (1190) | 2197 (1314) | 3356 (546) |
| Exposures | Mean (P5–P95) | ||||||
| CO (ppm) | 0.52 (0.34, 0.79) |
0.52 (0.32, 0.82) |
0.52 (0.30, 0.85) |
0.52 (0.29, 0.85) |
0.51 (0.28, 0.90) |
0.49 (0.27, 0.95) |
0.52 (0.34, 0.79) |
| NO2 (ppb) | 17.48 (12.48, 23.68) |
17.58 (12.30, 24.17) |
17.68 (12.16, 24.67) |
17.69 (11.91, 24.79) |
17.55 (10.92, 25.14) |
16.75 (9.15, 24.97) |
17.49 (12.44, 23.73) |
| PM10 (μg/m3) | 37.14 (24.67, 53.21) |
37.60 (24.34, 54.73) |
37.97 (24.14, 56.80) |
37.39 (23.36, 54.86) |
38.52 (22.82, 58.81) |
40.01 (23.87, 54.61) |
37.21 (24.62, 53.36) |
| PM2.5 (μg/m3) | 17.99 (10.84, 28.44) |
18.19 (10.30, 29.92) |
18.45 (10.06, 30.91) |
18.39 (9.56, 31.25) |
18.60 (9.24, 32.85) |
18.61 (9.11, 33.68) |
18.02 (10.75, 28.58) |
| Traffic density | 34.97 (0.00, 38.84) |
37.45 (0.00, 47.39) |
39.15 (0.00, 48.04) |
39.73 (0.00, 52.99) |
42.04 (0.00, 71.86) |
42.83 (0.00, 52.74) |
35.35 (0.00, 40.31) |
Abbreviations: SD, standard deviation; g, grams, P5–P95, 5th and 95th percentile
a
Percentages may not equal 100 owing to rounding.