Table 1.
Baseline Characteristics of Pregnant Women Included and Excluded From the Blood Cotinine (n = 662), Salivary Cotinine (n = 967), and Exhaled Carbon Monoxide (CO) (n = 1050) Analyses
| Characteristics | CO analysis (n = 1050) | Blood cotinine analysis | Salivary cotinine analysis | ||
|---|---|---|---|---|---|
| Included (n = 662) | Excluded (n = 388) | Included (n = 967) | Excluded (n = 83) | ||
| Age in years (M ± SD) | 26.3±6.2 | 26.8±6.2* | 25.6±6.0* | 26.3±6.2 | 26.2±6.0 |
| Gestational age in weeks (M ± SD) | 16.2±3.5 | 16.3±3.5 | 16.1±3.5 | 16.2±3.5 | 16.3±3.3 |
| Body mass index in kg/m2 (M ± SD)a | 27.0±6.2 | 26.8±5.7 | 27.2±7.0 | 27.0±6.2 | 26.0±6.3 |
| Ethnicity, n (%)b | |||||
| White British | 1018 (97.0%) | 643 (97.1%) | 375 (96.6%) | 940 (97.2%) | 78 (94.0%) |
| Others | 32 (3.0%) | 19 (2.9%) | 13 (3.4%) | 27 (2.8%) | 5 (6.0%) |
| Number of cigarettes smoked per day before pregnancy, (n) | |||||
| Median | 20 | 20 | 20 | 20 | 20 |
| Interquartile range | 15–20 | 15–20 | 15–20 | 15–20 | 15–20 |
| Number of cigarettes smoked per day at enrolment (n) | |||||
| Median | 13.5 | 13 | 15 | 13 | 15 |
| Interquartile range | 10–20 | 10–20 | 10–20 | 10–20 | 10–18 |
| Time from awakening to lighting first cigarette (min) | |||||
| Median | 10.0 | 10.0* | 7.0* | 10.0* | 7.0* |
| Interquartile range | 3.0–21.0 | 3.0–31.0 | 3.0–21.0 | 3.0–28.0 | 3.0–21.0 |
| Heaviness of Smoking Index, n (%) | |||||
| 0 | 65 (6.2%) | 45 (6.8%) | 20 (5.2%) | 61 (6.3%) | 4 (4.8%) |
| 1 | 134 (12.8%) | 91 (13.7%) | 43 (11.1%) | 128 (13.2%) | 6 (7.2%) |
| 2 | 259 (24.7%) | 161 (24.3%) | 98 (25.3%) | 238 (24.6%) | 21 (25.3%) |
| 3 | 321 (30.6%) | 202 (30.5%) | 119 (30.7%) | 295 (30.5%) | 26 (31.3%) |
| 4 | 209 (19.9%) | 132 (19.9%) | 77 (19.8%) | 186 (19.2%) | 23 (27.7%) |
| 5 | 52 (5.0%) | 29 (4.4%) | 23 (5.9%) | 50 (5.2%) | 2 (2.4%) |
| 6 | 10 (1%) | 2 (0.3%) | 8 (2.1%) | 9 (0.9%) | 1 (1.2%) |
| Blood cotinine (ng/ml)c | |||||
| Median | 127.1 | 127.1 | 142.3 | ||
| Interquartile range | 88.0–174.1 | 88.8–174.1 | 92.6–176.9 | ||
| Salivary cotinine (ng/ml)d | |||||
| Median | 121.5 | 120.5 | 124.0 | ||
| Interquartile range | 78.1–177.2 | 74.9–180.1 | 81.2–167.7 | ||
| Exhaled carbon monoxide (ppm) | |||||
| Median | 14 | 15 | 14 | 14 | 15 |
| Interquartile range | 11–20 | 11–21 | 11–19.8 | 11–20 | 11–21 |
| Women with partner who smokes, n (%)e | 716 (74.4%) | 439 (71.4%)* | 277 (79.6%)* | 662 (74.3%) | 54 (75.0%) |
| Previous use of nicotine replacement therapy during current pregnancy, n (%) | 47 (4.5%) | 27 (4.1%) | 20 (5.2%) | 41 (4.2%) | 6 (7.2%) |
Note. aBody mass index was not recorded for 22 women in the included group and 34 women in the excluded group (blood cotinine analysis); 47 women in the included group and 9 women in the excluded group (salivary cotinine analysis); 56 women in the overall group (exhaled CO analysis).
bSelf-reported ethnicity was categorized according to standard U.K. census category. “Other” included other White categories (e.g., White Irish or White other).
cThree hundred and thirty-nine women in the included group and 47 women in the excluded group (salivary cotinine analysis); 386 women in the overall group (exhaled CO analysis) did not have blood cotinine collected at the time of enrolment.
dThirty-four women in the included group and 46 women in the excluded group (blood cotinine analysis); 80 women in the overall group (exhaled CO analysis) did not have salivary cotinine collected at the time of enrolment.
eForty-seven women in the included group and 40 women in the excluded group (blood cotinine analysis); 76 women in the included group and 11 women in the excluded group (salivary cotinine analysis); 87 women in the overall group (exhaled CO analysis) did not have a partner at the time of enrolment.
*Difference in baseline characteristics between pregnant women included and excluded in the analyses was statistically significant (p < .05).