Table 1.
Characteristics of participants
| All | Maternal Fasting Plasma Cotinine concentration (ng/mL) | |||||
|---|---|---|---|---|---|---|
| Group 1 | Group 2 | Group 3 | Group 4 | |||
| <0.17 | <0.17 | 0.17-13.99 | ≥14 | |||
| Self-reported ETS Exposure | No | Yes | - | - | p value | |
| No. of Subjects, N (%) | 969 | 511 (52.7) | 282 (29.1) | 140 (14.4) | 36 (3.7) | |
| Maternal Characteristics | ||||||
| Ethnicity | <0.001b | |||||
| Chinese | 527 (54.4)a | 325 (61.7) | 141 (26.8) | 47 (8.9) | 14 (2.6) | |
| Malay | 260 (26.8)a | 62 (23.9) | 102 (39.2) | 78 (30.0) | 18 (6.9) | |
| Indian | 182 (18.8)a | 124 (68.1) | 39 (21.4) | 15 (8.2) | 4 (2.2) | |
| Maternal Age (years) | <0.001b | |||||
| 30 and below | 423 (43.7)a | 169 (40.0) | 139 (32.9) | 93 (22.0) | 22 (5.2) | |
| Above 30 | 546 (56.4)a | 342 (62.6) | 143 (26.2) | 47 (8.6) | 14 (2.6) | |
| Education level | <0.001b | |||||
| Secondary and below | 294 (30.3)a | 87 (29.6) | 114 (38.8) | 67 (22.8) | 26 (8.8) | |
| Diploma | 335 (34.6)a | 156 (46.6) | 116 (34.6) | 54 (16.1) | 9 (2.7) | |
| University and above | 327 (33.8)a | 263 (80.4) | 46 (14.1) | 18 (5.5) | 0 (0.0) | |
| Unknown | 13 (1.3)a | 5 (38.5) | 6 (46.2) | 1 (7.7) | 1 (7.7) | |
| Parity | <0.001b | |||||
| 0 | 412 (42.5)a | 212 (51.5) | 123 (29.9) | 70 (17.0) | 7 (1.7) | |
| 1 | 344 (35.5)a | 210 (61.1) | 86 (25.0) | 35 (10.2) | 13 (3.8) | |
| ≥ 2 | 213 (22.0)a | 89 (41.8) | 73 (34.3) | 35 (16.4) | 16 (7.5) | |
| Early pregnancy BMI (kg/m2) | 0.246b | |||||
| Less than 18.5 | 84 (8.7)a | 47 (56.0) | 21 (25.0) | 11 (13.1) | 5 (6.0) | |
| 18.5-22.9 | 439 (45.3)a | 242 (55.1) | 123 (28.0) | 57 (13.0) | 17 (3.9) | |
| 23-27.4 | 269 (27.8)a | 138 (51.3) | 84 (31.2) | 43 (16.0) | 4 (1.5) | |
| 27.5 and above | 168 (17.3)a | 78 (46.4) | 52 (31.0) | 29 (17.3) | 9 (5.4) | |
| Unknown | 9 (0.9)a | |||||
| Maternal height (cm)f | 158.3 (5.6) | 158.5 (5.7) | 158.1 (5.5) | 157.8 (5.7) | 158.6 (5.4) | 0.46 c |
| Offspring characteristics | ||||||
| Sex | 0.884b | |||||
| Female | 465 (48.0)a | 249 (53.6) | 131 (28.2) | 69 (14.8) | 16 (3.4) | |
| Male | 504 (52.0)a | 262 (52.0) | 151 (30.0) | 71 (14.1) | 20 (4.0) | |
| Birth Weight (gram)f | 3110±433 | 3138 ±429 | 3092 ±449 | 3112 ±382 | 2843 ± 467 | <0.001c |
| Birth Length (cm)f | 48.7 ±2.2 | 49.0 ±2.1 | 48.4 ±2.3 | 48.5 ±2.0 | 47.4 ±2.3 | <0.001c |
| Gestational age at birth (weeks)d, f | 38.8 ±1.3 | 39.0 ±1.2 | 38.7 ±1.2 | 38.7 ±1.2 | 38.2 ±1.6 | <0.001c |
| Postnatal ETS exposuree | ||||||
| No | 534 (55.1)a | 407 (76.2) | 92 (17.2) | 30 (5.6) | 5 (0.9) | <0.001b |
| Yes | 289 (29.8)a | 36 (12.5) | 146 (50.5) | 84 (29.1) | 23 (8.0) | |
| Unknown (N=146) | 146 (15.1)a | |||||
Percentage of all study subjects (N=969) across categories of each characteristic, otherwise the percentage (%) indicates distribution of each category across the four different prenatal tobacco exposure groups.
p value determined by chi-square (χ2) test
p value determined by ANOVA test
Pregnancy dating was done by first trimester crown rump length on ultrasound scan.
Without postnatal ETS exposure was defined as either having no smokers at home or if there is a smoker at home they only smoked far away from the house; With postnatal ETS exposure was defined as having at least a smoker at home who either smoked in front of the subject or who smoked within or just outside the house.
mean ± SD
Missing data: Unknown data for maternal BMI in the 1st trimester (n=49) were imputed by self-reported pre-pregnancy BMI (n=40) or estimated using the maternal pregnancy BMI at 26-28 week (n=5); for maternal education level (n=13) were imputed by mode (diploma) in further analysis.