Table 2.

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.