Table 2.
Baseline characteristics and demographics
| Cases | Controls | ||
|---|---|---|---|
| Number of children | 15 795 | 724 623 | |
| Mothers | |||
| Age at giving birth, y | Mean (SD) | 28 (1.5) a | 29 (1.5) |
| Median (IQR) | 28 (23‐32) | 29 (24‐33) | |
| Mother's SIMD quintile, n/N (%) | 1 – most deprived | 4992/15 758 (31.7) a | 185 494/722 908 (25.7) |
| 2 | 3404/15 758 (21.6) b | 148 955/722 908 (20.6) | |
| 3 | 2684/15 758 (17.0) a | 133 638/722 908 (18.5) | |
| 4 | 2409/15 758 (15.3) a | 129 472/722 908 (17.9) | |
| 5 – least deprived | 2269/15 758 (14.4) a | 125 349/722 908 (17.3) | |
| Mother's smoking history at predelivery assessment, n/N (%) | Current | 5234/14 271 (36.7) a | 169 931/656 611 (25.9) |
| Former | 1248/14 271 (8.7) a | 66 310/656 611 (10.1) | |
| Never | 7789/14 271 (54.6) a | 420 370/656 611 (64.0) | |
| Mother's previous pregnancies, n/N (%) | 0 | 3948/15 795 (25.0) a | 262 133/724 621 (36.2) |
| 1 | 5155/15 795 (32.6) c | 225 966/724 621 (31.2) | |
| 2+ | 6692/15 795 (42.4) c | 236 522/724 621 (32.6) | |
| Children and births | |||
| Sex, n/N (%) | Male | 8934/15 793 (56.6) a | 369 792/724 596 (51.0) |
| Multiple births, n/N (%) | Multiple | 857/15 793 (5.4) a | 20 271/724 599 (2.8) |
| Emergency cesarean | |||
| n/N (%) | Yes | 2527/15 795 (16.0) a | 103 637/724 623 (14.3) |
| Gestational age at birth, wk | Mean (SD) | 38 (0.3) a | 39 (0.3) |
| Median (IQR) | 39 (37‐40) | 40 (39‐41) | |
| Birth weight, g | Mean (SD) | 3162 (143) a | 3381 (117) |
| Median (IQR) | 3270 (2790‐3660) | 3410 (3050‐3760) | |
| Comorbidities, n/N (%) | Any comorbidity d | 1269/15 795 (8.0) a | 10 566/724 623 (1.5) |
Abbreviations: IQR, interquartile range; RSV, respiratory syncytial virus; SD, standard deviation; SIMD, Scottish Index of Multiple Deprivation.
a
P < .0001 vs control group.
b
P < .01 vs control group.
c
P < .0001 for combined ≥1 pregnancies vs control group.
d
Diagnosis with any predefined comorbidity as detailed in Table 1.