Table 1. Characteristics of case and comparison women.
| Independent Variables | Number (%) of cases (n = 405) | Number (%) of comparison women (n = 694) | OR (95% CI, P-value) | aORa (95% CI, P-value) |
|---|---|---|---|---|
| Maternal age (years) | ||||
| <20 | 14 (3) | 18 (3) | 1·30 (0·64–2·65, p = 0.475) | - |
| 20–35 | 286 (71) | 477 (69) | 1.00 (-) | - |
| ≥ 35 | 105 (26) | 199 (29) | 0·88 (0·67–1·16, p = 0.368) | - |
| Socioeconomic status | ||||
| Professional | 61 (15) | 143 (21) | 0·72 (0·51–1·01, p = 0.003) | 0·59 (0·39–0·89, p = 0.013) |
| Non-professional employed | 233 (58) | 394 (57) | 1·00 (-) | 1·00 (-) |
| Unemployed | 64 (16) | 76 (11) | 1·42 (0·98–2·06, p = 0.061) | 1·23 (0·79–1·92, p = 0.354) |
| Unknown | 47 (12) | 81 (12) | - | |
| Marital Status | ||||
| Married/Cohabiting | 327 (81) | 588 (85) | 1·00 (-) | - |
| Single | 76 (19) | 96 (14) | 1·42 (1·02–1·98, p = 0.036) | - |
| Unknown | 2 (0) | 10 (1) | ||
| Smoking Status during pregnancy | ||||
| Did not smoke | 317 (78) | 549 (79) | 1·00 (-) | - |
| Smoked | 86 (21) | 135 (19) | 1·10 (0·81–1·49, p = 0.526) | - |
| Unknown | 2 (0) | 10 (1) | ||
| Parity | ||||
| Nulliparous | 129 (32) | 274 (39) | 0·72 (0·55–0·93, p = 0.011) | - |
| Multiparous | 276 (68) | 420(61) | 1·00 (-) | - |
| Body Mass Index | ||||
| Normal or overweight (<30 kg/m2) | 282 (70) | 518 (75) | 1·00 (-) | - |
| Obese (≥30 kg/m2) | 116 (29) | 155 (22) | 1·37 (1·04–1·82, p = 0.026) | - |
| Unknown | 7 (2) | 21 (3) | ||
| Multiple Pregnancy | ||||
| Yes | 12 (3) | 13 (2) | 1·60 (0·72–3·54, p = 0.246) | - |
| No | 393 (97) | 681 (98) | 1·00 (-) | - |
| Pre-existing medical condition | ||||
| Yes | 56 (14) | 77 (11) | 1·29 (0·89–1·86, p = 0.182) | - |
| No | 348 (86) | 615 (89) | 1·00 (-) | - |
| Unknown | 1 (0) | 2 (0) | ||
| Pre-existing Asthma | ||||
| Yes | 41 (10) | 30 (4) | 2·50 (1·53–4.07, p = 0.041) | 2·42 (1·30–4·49, p = 0.005) |
| No | 363 (90) | 663 (96) | 1·00 (-) | 1·00 (-) |
| Unknown | 1 (0) | 1 (0) | ||
| Known previous pregnancy complications | ||||
| Yes | 43 (11) | 35 (5) | 2·24 (1·41–3·56, p = 0.001) | 2·47 (1·33–4·61, p = 0.004) |
| No | 362 (89) | 659 (95) | 1·00 (-) | 1·00 (-) |
| Immunization Status | ||||
| Ever Immunised against influenza | ||||
| Yes | 137 (34) | 267 (38) | 0·69 (0·53–0·92, p = 0.010) | - |
| No | 190 (47) | 257 (37) | 1·00 (-) | - |
| Unknown | 78 (19) | 170 (25) | ||
| Immunised in the relevant influenza season | ||||
| Yes | 106 (26) | 214 (31) | 0·65 (0·48–0·87, p = 0.004) | 0·62 (0·45–0·86, p = 0.004) |
| No | 202 (50) | 264 (38) | 1·00 (-) | 1·00 (-) |
| Unknown | 97 (24) | 216 (31) |
aOR adjusted for Asthma requiring regular steroid treatment, Immunization status, Employment status, and relevant previous pregnancy problems.