Main characteristics of the study population
| First trimester | Third trimester | |||
| antibiotics | antibiotics | |||
| No | Yes | No | Yes | |
| Subjects | 3301 (93.5) | 229 (6.5) | 3729 (93.6) | 256 (6.4) |
| Maternal educational level | ||||
| University degree or higher | 2031 (61.5) | 150 (65.5) | 2292 (61.5) | 165 (64.5) |
| Secondary school | 1132 (34.3) | 69 (30.1) | 1271 (34.1) | 82 (32.0) |
| Primary school or less | 138 (4.2) | 10 (4.4) | 166 (4.4) | 9 (3.5) |
| Maternal age at childbirth years | ||||
| <30 | 654 (19.8) | 44 (19.2) | 727 (19.5) | 43 (16.8) |
| 30–34 | 1462 (44.3) | 86 (37.5) | 1634 (43.8) | 110 (43.0) |
| 35–39 | 977 (29.6) | 70 (30.6) | 1113 (29.9) | 86 (33.6) |
| ≥40 | 208 (6.3) | 29 (12.7) | 255 (6.8) | 17 (6.6) |
| Maternal asthma/asthmatic bronchitis | ||||
| Yes | 247 (7.5) | 20 (8.7) | 276 (7.4) | 25 (9.8) |
| No | 3054 (92.5) | 209 (91.3) | 3453 (92.6) | 231 (90.2) |
| Siblings | ||||
| Yes | 975 (29.5) | 95 (41.5) | 1200 (32.2) | 102 (39.8) |
| No | 2326 (70.5) | 134 (58.5) | 2529 (67.8) | 154 (60.2) |
| Maternal smoking in pregnancy | ||||
| Yes | 257 (7.8) | 20 (8.7) | 289 (7.7) | 20 (7.8) |
| No | 3044 (92.2) | 209 (91.3) | 3440 (92.3) | 236 (92.2) |
| Maternal paracetamol use in pregnancy | ||||
| Yes | 1752 (53.1) | 148 (64.6) | 1989 (53.3) | 174 (68.0) |
| No | 1549 (46.9) | 81 (35.4) | 1740 (46.7) | 82 (32.0) |
| Maternal respiratory infections in pregnancy | ||||
| Otitis and/or sinusitis and/or throat infections | ||||
| Yes | 278 (8.4) | 60 (26.2) | 201 (5.4) | 66 (25.8) |
| No | 3023 (91.6) | 169 (73.8) | 3528 (94.6) | 190 (74.2) |
| Bronchitis and/or flu | ||||
| Yes | 175 (5.3) | 33 (14.4) | 153 (4.1) | 48 (18.7) |
| No | 3126 (94.7) | 196 (85.6) | 3576 (95.9) | 208 (81.3) |
| Common cold | ||||
| Yes | 621 (18.8) | 48 (21.0) | 463 (12.4) | 67 (26.2) |
| No | 3680 (81.2) | 181 (79.0) | 3266 (87.6) | 189 (73.8) |
| Other maternal infections in pregnancy | ||||
| Urinary infections and/or urinary burning | ||||
| Yes | 122 (3.7) | 46 (20.1) | 202 (5.4) | 70 (27.3) |
| No | 3179 (96.3) | 183 (79.9) | 3527 (94.6) | 186 (72.7) |
| Vaginal infections | ||||
| Yes | 194 (5.9) | 62 (27.1) | 353 (9.5) | 80 (31.2) |
| No | 3107 (94.1) | 167 (72.9) | 3373 (90.5) | 176 (68.8) |
| Fever >38oC | ||||
| Yes | 90 (2.7) | 22 (9.6) | 58 (1.6) | 29 (11.3) |
| No | 3211 (97.3) | 207 (90.4) | 3671 (98.4) | 227 (88.7) |
| Mode of delivery | ||||
| Vaginal | 2254 (74.3) | 136 (65.4) | 2548 (74.0) | 159 (67.7) |
| Caesarean section | 779 (25.7) | 72 (34.6) | 895 (26.0) | 76 (32.3) |
| Wheezing up to 6 months | ||||
| Yes | 220 (7.1) | 22 (10.6) | 268 (7.3) | 34 (13.4) |
| No | 2887 (92.9) | 185 (89.4) | 3410 (92.7) | 219 (86.6) |
| Ever-wheezing up to 18 months | ||||
| Yes | 690 (20.9) | 60 (26.2) | 803 (21.5) | 74 (28.9) |
| No | 2611 (79.1) | 169 (73.8) | 2926 (78.5) | 182 (71.1) |
| Recurrent wheezing | ||||
| Yes | 118 (3.8) | 12 (5.7) | 134 (3.8) | 24 (10.4) |
| No | 2989 (96.2) | 200 (94.3) | 3371 (96.2) | 207 (89.6) |
Data are presented as n (%).