Characteristics of 39 420 infants born during 32–36 weeks of gestation with and without infant respiratory distress syndrome (IRDS), between 1 January 1997 and 31 December 2007 in Denmark
| IRDS, n (%) | No IRDS, n (%) | |
|---|---|---|
| All | 2255 (100.0) | 37 165 (100.0) |
| Gestational age (week of gestation) | ||
| 32 | 602 (26.7) | 2058 (5.5) |
| 33 | 545 (24.2) | 3313 (8.9) |
| 34 | 526 (23.3) | 5652 (15.2) |
| 35 | 346 (15.3) | 9156 (24.6) |
| 36 | 236 (10.5) | 16 986 (45.7) |
| Birth year | ||
| 1997–1999 | 534 (23.7) | 9379 (25.2) |
| 2000–2002 | 602 (26.7) | 10 443 (28.1) |
| 2003–2005 | 696 (30.9) | 10 433 (28.1) |
| 2006–2007 | 423 (18.8) | 6910 (18.6) |
| Gender | ||
| Female | 897 (39.8) | 17 184 (46.2) |
| Male | 1358 (60.2) | 19.981 (53.8) |
| Apgar score at 5 min | ||
| Low (0–6) | 111 (4.9) | 646 (1.7) |
| Intermediate (7–8) | 271 (12.0) | 1824 (4.9) |
| Normal (9–10) | 1816 (80.5) | 33 974 (91.4) |
| Missing | 57 (2.5) | 721 (1.9) |
| Multiplicity | ||
| Singleton | 1644 (72.9) | 27 438 (73.8) |
| Twin | 611 (27.1) | 9727 (26.2) |
| Epilepsy | 53 (2.4) | 590 (1.6) |
| Major malformation (<1 year) | 217 (9.6) | 2525 (6.8) |
| Mother's age at delivery | ||
| <18 years | 5 (0.2) | 130 (0.4) |
| 18–34 years | 1807 (80.1) | 30 131 (81.1) |
| ≥35 years | 443 (19.7) | 6903 (18.6) |
| Missing | 0 (0.0) | 1 (0.0) |
| Maternal smoking status | ||
| Non smoker/former smoker | 1689 (74.9) | 26 487 (71.3) |
| Smoker | 403 (17.9) | 8433 (22.7) |
| Missing | 163 (7.2) | 2245 (6.0) |
| Bronchopulmonary dysplasia (BPD) (<1 year) | ||
| Yes | 22 (1.0) | 16 (0.1) |
| Intracerebral haemorrhage /intraventricular haemorrhage (ICH/IVH) (<30 days)* | ||
| Yes | 46 (2.0) | 121 (0.3) |
| Necrotising enterocolitis (NEC) (<30 days) | ||
| Yes | 20 (0.9) | 59 (0.2) |
| Patent ductus arteriosus (PDA) (<30 days) | ||
| Yes | 77 (3.4) | 239 (0.6) |
| Other diseases† | ||
| Yes | 682 (30.2) | 6641 (17.9) |
*Information on total number of infants undergoing cranial ultrasound examination is unavailable.
†Other diseases whose symptoms may overlap with those of IRDS, occurring within 4 days of birth (perinatal breathing disorders other than IRDS, congenital heart diseases, and viral and bacterial infections).