Table 1.

Preterm birth (PTB) and duration of gestation by maternal demographic and pregnancy-related characteristics among MIREC study participants in Canada, 2008–2011

	n (%)	PTB (%)	Duration of gestation 25th percentile	Duration of gestation Median (IQR)
Total	1857 (100%)	115 (100%)	38.6	39.6 (1.8)
Maternal age
19–24	117 (6.3%)	9 (7.8%)	38.4	39.9 (1.9)
25–29	443 (24.0%)	18 (15.7%)	38.9	39.9 (1.7)
30–34	656 (35.5%)	38 (33.0%)	38.6	39.6 (2.0)
35–39	502 (27.2%)	39 (33.9%)	38.6	39.3 (1.8)
40+	127 (6.9%)	10 (8.7%)	38.8	39.4 (1.5)
Education
High school diploma or less	161 (8.7%)	11 (9.6%)	38.4	39.4 (1.9)
Some college, trade school, or college diploma	538 (29.0%)	40 (34.8%)	38.4	39.4 (1.9)
Undergrad degree	681 (36.7%)	37 (34.8%)	38.7	39.7 (1.9)
Graduate degree	475 (25.6%)	27 (23.5%)	38.7	39.6 (1.9)
Race
White	1517 (81.7%)	91 (79.1%)	38.6	39.6 (2.0)
Other	340 (18.3%)	24 (20.9%)	38.4	39.3 (1.7)
Marital status
Married	1337 (72.0%)	78 (67.8%)	38.6	39.6 (1.8)
Same partner for ≥ 1 year	432 (23.3%)	30 (26.1%)	38.6	39.7 (2.0)
Single	78 (4.2%)	6 (5.2%)	38.5	39.6 (1.7)
Others	10 (0.5%)	1 (0.9%)	38.9	39.1 (0.4)
Parity
0	812 (43.7%)	52 (45.2%)	38.9	39.9 (1.8)
1	751 (40.4%)	47 (40.9%)	38.6	39.4 (1.7)
2	222 (12.0%)	13 (11.3%)	38.3	39.3 (1.8)
3+	72 (3.9%)	3 (2.6%)	38.4	39.0 (1.6)
Smoking status
Never	1137 (61.3%)	71 (61.7%)	38.6	39.4 (1.8)
Former	498 (26.8%)	30 (26.1%)	38.7	39.7 (1.9)
Quit during pregnancy	115 (6.2%)	8 (7.0%)	38.6	39.6 (2.0)
Current	106 (5.7%)	6 (5.2%)	38.6	39.6 (1.8)
BMI
Underweight	49 (2.9%)	2 (1.7%)	38.6	39.4 (1.8)
Normal	1040 (60.5%)	52 (45.2%)	38.9	39.6 (1.7)
Overweight	372 (21.6%)	20 (17.4%)	38.6	39.6 (2.0)
Obese	258 (15.0%)	33 (28.7%)	38.1	39.1 (2.2)

Numbers may not sum to total as a result of missing data