Table 1 Maternal and infant characteristics of cohort participants
Characteristics | Preterm birth | Term birth | Low birth weight | Normal birth weight | |
|---|---|---|---|---|---|
n (%a) | n (%a) | n (%a) | n (%a) | ||
Maternal | Â | Â | Â | Â | Â |
 Age (years) | Mean (95%CI) | 30.6 (29.9 to 31.2) | 30.5 (30.4 to 30.8) | 30.4 (29.6 to 31.3) | 30.6 (30.4 to 30.8) |
 Highest level of education | High school or less | 20 (10.7) | 244 (9.6) | 15 (12.2) | 240 (9.7) |
| Â | Some trade schooling, college or university | 23 (12.3) | 346 (13.6) | 16 (13.0) | 329 (13.3) |
| Â | Graduated trade school, college, university | 111 (59.4) | 1,554 (61.1) | 75 (61.0) | 1,512 (61.1) |
| Â | Some graduate school, completed graduate school | 33 (17.7) | 399 (15.7) | 17 (13.8) | 394 (15.9) |
 Household income | <$40,000 | 23 (12.8) | 182 (7.4) | 17 (14.4) | 181 (7.5) |
| Â | $40,000 to <$60,000 | 24 (13.3) | 201 (8.1) | 14 (11.9) | 200 (8.3) |
| Â | $60,000 to <$80,000 | 24 (13.3) | 312 (12.6) | 17 (14.4) | 293 (12.2) |
| Â | $80,000 to <$100,000 | 24 (13.3) | 448 (18.1) | 19 (16.1) | 427 (17.7) |
|  | ≥$100,000 | 85 (47.2) | 1,330 (53.8) | 51 (43.2) | 1,308 (54.3) |
 Pre-pregnancy BMI | Underweight (< 18.5 kg/m2) | 6 (3.2) | 116 (4.6) | 6 (4.9) | 116 (4.8) |
| Â | Normal weight (18.5-<25.0Â kg/m2) | 114 (61.6) | 1,574 (62.8) | 78 (63.9) | 1,518 (62.2) |
| Â | Overweight (25.0-<30.0Â kg/m2) | 38 (20.5) | 553 (22.1) | 23 (18.9) | 540 (22.1) |
|  | Obese (≥ 30.0 kg/m2) | 27 (14.6) | 265 (10.6) | 15 (12.3) | 266 (10.9) |
 Parity | No | 97 (52.7) | 1,196 (47.2) | 74 (60.2) | 1,164 (47.2) |
| Â | Yes | 87 (47.3) | 1,337 (52.8) | 49 (39.8) | 1,300 (52.8) |
Smoking | Â | Â | Â | Â | Â |
 Smoking during pregnancy | No | 139 (84.2) | 2,085 (89.3) | 88 (83.0) | 2,030 (89.3) |
| Â | Yes | 26 (15.8) | 249 (10.7) | 18 (17.0) | 244 (10.7) |
 Days per week smoked during pregnancyb | < 1 day per week | 12 (54.6) | 144 (60.0) | 9 (56.3) | 142 (60.9) |
|  | ≥ 1 day per week | 10 (45.5) | 96 (40.0) | 7(43.8) | 91 (39.1) |
 Cigarettes smoked per day (on average) during pregnancyb | < 1 cigarettes | 14 (63.6) | 149 (62.3) | 11 (68.8) | 147 (63.1) |
|  | 1–10 cigarettes | 8 (36.4) | 81 (33.9) | 5 (31.3) | 76 (32.6) |
|  | > 11 cigarettes | 0 (0.0) | 9 (3.8) | 0 (0.0) | 10 (4.3) |
 Frequency partner smokes | Not at all | 146 (79.4) | 2,147 (85.3) | 93 (76.9) | 2,083 (85.1) |
| Â | Occasionally | 14 (7.6) | 148 (5.9) | 13 (10.7) | 141 (5.8) |
| Â | Daily | 24 (13.0) | 223 (8.9) | 15 (12.4) | 223 (9.1) |
 Smoking currently handled | Non-smoking home | 129 (71.7) | 1,684 (67.5) | 82 (71.3) | 1,648 (67.8) |
| Â | No smoking inside home or with various restrictions | 51 (28.3) | 810 (32.5) | 33 (28.7) | 784 (32.2) |
 Total smoke exposure | None | 118 (69.4) | 1,841 (78.5) | 70 (64.2) | 1,790 (78.4) |
| Â | Environmental tobacco smoke and/or active smoke | 52 (30.6) | 503 (21.5) | 39 (35.8) | 492 (21.6) |
Stress | Â | Â | Â | Â | Â |
 Perceived Stress Scale total score   < 25 weeks gestation | Median (IQR) | 14 (11 to 19) | 13 (9 to 17) | 15 (12 to 20) | 13 (9 to 17) |
 Perceived Stress Scale total score   34–36 weeks gestation |  | 14 (9 to 20) | 13 (8 to 17) | 14 (10 to 20) | 13 (8 to 17) |
 Spielberger State Anxiety Inventory total score   < 25 weeks gestation | Median (IQR) | 31 (25.5 to 38) | 29 (24 to 35) | 32 (25 to 41) | 29 (24 to 35) |
 Spielberger State Anxiety Inventory total score   34–36 weeks gestation |  | 36 (29 to 42) | 30 (25 to 37) | 33.5 (28 to 45) | 30 (25 to 37) |