Table 1.
Baseline characteristics of pregnant smokers using stop smoking services in the trial, by study group for randomised and analysed populations. Data are number (%) of participants unless otherwise stated
| Characteristic | All randomised participants* (n=944) | Participants who provided smoking status at the primary outcome stage (n=843) | |||
|---|---|---|---|---|---|
| Financial incentives (n=472) | Control (n=472) | Financial incentives (n=412) | Control (n=431) | ||
| Body mass index: | |||||
| No (%) of participants | 434 (91.9) | 449 (94.5) | 381 (92.5) | 412 (95.6) | |
| Mean (standard deviation) | 27.44 (6.35) | 26.76 (6.18) | 27.44 (6.32) | 26.85 (6.23) | |
| Ethnic group: | |||||
| White | 466 (98.7) | 464 (98.3) | 407 (98.8) | 426 (98.8) | |
| Mixed/multiple ethnic groups | 3 (0.6) | 3 (0.6) | 3 (0.7) | 3 (0.7) | |
| African/Caribbean/Black | 1 (0.2) | 1 (0.2) | 1 (0.2) | 1 (0.2) | |
| Asian/Asian British | 1 (0.2) | 1 (0.2) | 1 (0.2) | 0 (0) | |
| Missing | 1 (0.2) | 3 (0.6) | 0 (0) | 1 (0.2) | |
| Maternal age at randomisation (years): | |||||
| No (%) of participants | 471 (99.8) | 470 (99.6) | 412 (100) | 431 (100) | |
| Mean (standard deviation) | 27.92 (5.71) | 27.89 (5.86) | 28.06 (5.60) | 28.00 (5.91) | |
| Previous live births: | |||||
| No (%) of participants | 448 (94.9) | 454 (96.2) | 406 (98.5) | 426 (98.8) | |
| Mean (standard deviation) | 2.1 (1.3) | 2.2 (1.3) | 2.1 (1.3) | 2.2 (1.4) | |
| Gestational age at maternity booking, weeks: | |||||
| No (%) of participants | 446 (94.5) | 440 (93.2) | 393 (95.4) | 403 (93.5) | |
| Mean (standard deviation) | 11.3 (3.3) | 11.3 (3.2) | 11.3 (3.3) | 11.2 (3.3) | |
| Index of multiple deprivation (divided by quintile: | |||||
| Group 1 (most deprived) | 203 (43.0) | 199 (42.2) | 174 (42.2) | 181 (42.0) | |
| Group 2 | 132 (28.0) | 131 (27.8) | 120 (29.1) | 125 (29.0) | |
| Group 3 | 74 (15.7) | 71 (15.0) | 62 (15.0) | 64 (14.8) | |
| Group 4 | 33 (7.0) | 32 (6.8) | 30 (7.3) | 25 (5.8) | |
| Group 5 (least deprived) | 15 (3.2) | 19 (4.0) | 12 (2.9) | 19 (4.4) | |
| Missing | 15 (3.2) | 20 (4.2) | 14 (3.4) | 17 (3.9) | |
| Carbon monoxide reading at maternity booking (ppm): | |||||
| No (%) of participants | 323 (68.4) | 291 (61.7) | 281 (68.2) | 257 (59.6) | |
| Mean (standard deviation) | 9.7 (7.3) | 9.6 (6.7) | 9.7 (7.2) | 9.6 (6.6) | |
| Fagerström score: | |||||
| No (%) of participants | 454 (96.2) | 446 (94.5) | 396 (96.1) | 409 (94.9) | |
| Mean (standard deviation) | 4.1 (2.1) | 4.0 (2.2) | 4.1 (2.1) | 4.0 (2.2) | |
| No of cigarettes smoked a day at enrolment: | |||||
| ≤10 | 282 (59.7) | 279 (59.1) | 241 (58.5) | 251 (58.2) | |
| 11-20 | 165 (35.0) | 168 (35.6) | 149 (36.2) | 157 (36.4) | |
| 21-30 | 22 (4.7) | 21 (4.4) | 20 (4.9) | 21 (4.9) | |
| ≥31 | 2 (0.4) | 2 (0.4) | 2 (0.5) | 2 (0.5) | |
| Missing | 1 (0.2) | 2 (0.4) | 0 (0) | 0 (0) | |
| Partner smokes: | |||||
| Yes | 286 (60.6) | 271 (57.4) | 248 (60.2) | 249 (57.8) | |
| No | 177 (37.5) | 190 (40.3) | 157 (38.1) | 173 (40.1) | |
| Missing | 9 (2.1) | 11 (2.3) | 7 (1.7) | 9 (2.1) | |
| Age when participant started smoking (years): | |||||
| No (%) of participants | 471 (99.8) | 470 (99.6) | 412 (100) | 431 (100) | |
| Mean (standard deviation) | 14.7 (3.0) | 14.8 (2.8) | 14.7 (3.0) | 14.8 (2.8) | |
| Uses nicotine replacement therapy: | |||||
| Yes | 175 (37.1) | 176 (37.3) | 161 (39.1) | 164 (38.1) | |
| No | 296 (62.7) | 294 (62.3) | 251 (60.9) | 267 (61.9) | |
| Missing | 1 (0.2) | 2 (0.4) | 0 (0) | 0 (0) | |
| Uses electronic cigarettes: | |||||
| Yes | 88 (18.6) | 83 (17.6) | 79 (19.2) | 74 (17.2) | |
| No | 383 (81.1) | 387 (82.0) | 333 (80.8) | 357 (82.8) | |
| Missing | 1 (0.2) | 2 (0.4) | 0 | 0 | |
Ppm=parts per million.
*
Three participants who requested their data be removed from the trial database after withdrawing are included in the denominator when reporting the percentage of non-missing data (eg, the missing data for cigarettes smoked a day at enrolment is from the three participants who requested their data be removed after withdrawing).