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Table 1 Demographic characteristics and crude odds ratios (95% CI) for preterm birth.a

From: Traffic-related air toxics and preterm birth: a population-based case-control study in Los Angeles county, California

Parameter Preterm Cases
(N = 10,265)
n (%) or mean ± SD
Cohort
(N = 111,203)
n (%) or mean ± SD
Crude Preterm OR (95% CI)
Gestational age (days) 244 (17.0) 275 (14.6) --
--
--
Birth weight (g) 2970 (643) 3342 (489) --
Infant's sex    
Female 4790 (46.7) 54665 (49.2) 0.91 (0.88-0.95)
Male 5474 (53.3) 56537 (50.8) 1.00
Missing 1 1  
Maternal age (years)    
< 20 1336 (13.0) 13185 (11.9) 1.15 (1.08-1.24)
20-24 2555 (24.9) 28409 (25.6) 1.03 (0.97-1.09)
25-29 2556 (24.9) 29508 (26.5) 1.00
30-34 2121 (20.7) 24347 (21.9) 0.99 (0.94-1.06)
≥ 35 1697 (16.5) 15751 (14.2) 1.26 (1.18-1.35)
Missing   3  
Maternal race/ethnicity    
Hispanic 7749 (75.8) 83947 (75.7) 1.36 (1.25-1.47)
White, non-Hispanic 588 (5.8) 8696 (7.8) 1.00
African American 1014 (9.9) 8472 (7.6) 1.79 (1.62-1.98)
Asian 474 (4.6) 5938 (5.4) 1.19 (1.05-1.34)
Otherb 398 (3.9) 3839 (3.5) 1.47 (1.29-1.66)
Missing 42 311  
Maternal education (years)    
≤ 8 1854 (18.2) 18169 (16.5) 1.09 (1.03-1.15)
9-12 5948 (58.6) 61957 (56.1) 1.00
13-15 1422 (14.0) 16605 (15.1) 0.88 (0.83-0.94)
≥ 16 935 (9.2) 13635 (12.3) 0.71 (0.66-0.77)
Missing 106 837  
Parity    
0 3535 (34.5) 41376 (37.2) 0.88 (0.84-0.92)
1 or more 6724 (65.5) 69787 (62.8) 1.00
Missing 6 40  
Prenatal care    
No prenatal care or started after 1st trimester 1287 (12.6) 10060 (9.1) 1.51 (1.41-1.60)
Started in first trimester 8935 (87.4) 100784 (90.9) 1.00
Missing 43 359  
Mother's birthplace (U.S. vs outside U.S.)    
U.S. Born 4096 (40.0) 42933 (38.6) 1.06 (1.01-1.10)
Foreign Born 6158 (60.0) 68187 (61.4) 1.00
Missing 11 83  
Mother's birthplace    
U.S. 4096 (40.0) 42933 (38.6) 1.00
Mexico 4048 (39.5) 45090 (40.6) 0.94 (0.90-0.98)
Other outside U.S. (includes Puerto Rico) 2110 (20.5) 23097 (20.8) 0.96 (0.91-1.01)
Missing 11 83  
Primary payment for prenatal care    
Private insurance/HMO/Pre-paid/Blue Cross-Blue Shield 2415 (23.9) 31685 (28.8) 1.00
Medi-Cal, other government programs, self pay, no care 7670 (76.1) 78283 (71.2) 1.30 (1.24-1.36)
Missing 180 1235  
Census-based SES index (quintiles)    
Q1 7237 (70.5) 74587 (67.1) 1.63 (1.32-2.02)
Q2 1710 (16.7) 19319 (17.4) 1.49 (1.20-1.85)
Q3 863 (8.4) 10737 (9.7) 1.35 (1.08-1.69)
Q4 364 (3.5) 5062 (4.5) 1.19 (0.94-1.50)
Q5 91 (0.89) 1498 (1.3) 1.00
  1. a Includes 10,265 preterm cases from the cohort of 111,203 births during June 1, 2004 to March 31, 2006 to women residing within five miles of a MATES air toxics monitoring station. Term LBW infants were eligible as preterm controls. Crude odds ratios are based on univariate conditional logistic regression analyses which take matching on gestational age into account.
  2. b Includes Native American/American Indian, Indian, Filipino, Hawaiian, Guamanian, Samoan, Eskimo, Aleut, Pacific Islander, Other (specified).