Neonatal characteristics of the study population, divided by history of NEC
| Reference individuals | NEC individuals | χ2 test* | |
| Total, n (%) | 3656 (100) | 720 (100) | |
| Variable | |||
| Category | |||
| Gender | |||
| Male | 2006 (54.9) | 394 (54.7) | 0.94 |
| Female | 1650 (45.1) | 326 (45.3) | |
| Degree of prematurity (gestational weeks)† | |||
| 32–42 | 1529 (41.8) | 255 (35.4) | <0.01 |
| 28–31 | 1065 (29.1) | 196 (27.2) | |
| <28 | 1062 (29.1) | 269 (37.4) | |
| Mean (weeks) | 31.3 | 30.5 | |
| Median | 30 | 29 | |
| Birth weight category (g) | |||
| ≥1500 | 1843 (50.4) | 282 (39.2) | <0.01 |
| <1500 | 1771 (48.4) | 420 (58.3) | |
| Missing | 42 (1.1) | 18 (2.5) | |
| Size relative to gestational age (GA)‡ | |||
| LGA and AGA | 3060 (83.7) | 544 (75.6) | <0.01 |
| SGA | 596 (16.3) | 176 (24.4) | |
| Perinatal asphyxia§ | |||
| No | 2916 (79.8) | 532 (73.9) | <0.01 |
| Yes | 590 (16.1) | 141 (19.6) | |
| Missing | 150 (4.1) | 47 (6.5) | |
| Abdominal surgery¶ | |||
| No | 3574 (97.8) | 563 (78.2) | <0.01 |
| Yes | 82 (2.2) | 157 (21.8) | |
| Birth cohort (year)** | |||
| 1987–1993 | 1052 (28.8) | 189 (26.3) | 0.34 |
| 1994–2001 | 806 (22.1) | 162 (22.5) | |
| 2002–2006 | 1015 (27.8) | 196 (27.2) | |
| 2007–2009 | 783 (21.4) | 173 (24.0) | |
| Region in Sweden | |||
| Rest of Sweden | 2852 (78.0) | 465 (64.6) | <0.01 |
| Stockholm county | 804 (22.0) | 255 (35.4) | |
| Presence of intestinal failure¶ | |||
| No | 3640 (99.6) | 677 (94.0) | <0.01 |
| Yes | 16 (0.44) | 43 (6.0) | |
| Presence of neonatal death†† | |||
| No | 3351 (91.7) | 613 (85.1) | <0.01 |
| 305 (8.3) | 107 (14.9) |
*P value <0.05 was considered significant.
†GA in weeks.
‡Size in relation to GA: LGA or AGA, and SGA.
§Apgar <7 at or more than 5 min.
¶) Defined by International Statistical Classification of Diseases and Related Health Problems codes versions 9 and 10.
**Based on infant’s birth year.
††Registered in the Causes of Death Register, during the neonatal period (≤28 days of age).
AGA, appropriate for GA; LGA, large for GA; NEC, necrotising enterocolitis; SGA, small for GA.