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Table 1 Baseline characteristics of cases and matched controls for NEC (matching factors highlighted)

From: Application of the matched nested case-control design to the secondary analysis of trial data

 Cases
(severe NEC)
(n = 35)
Matched controls
(n = 140)a
Non-cases
(n = 363)
Allocated to early arm, n (%)17 (48.6)74 (52.9)182 (50.1)
Male sex, n (%)20 (57.1)80 (57.1)193 (53.2)
Gestational age (weeks)
 Median (IQR)29 (27 to 31)29 (28 to 31)32 (29 to 33)
  < 29 weeks16 (45.7)61 (43.6)69 (19.0)
  > =29 weeks19 (54.3)79 (56.4)294 (81.0)
Birth weight (grams)
 Median (IQR)750 (660 to 931)780 (695 to 890)1030 (810 to 1280)
  < 750 g17 (48.6)53 (37.9)57 (15.7)
  > =750 g18 (51.4)87 (62.1)306 (84.3)
Multiple pregnancy, n (%)
 Twins5 (14.3)26 (18.6)83 (22.9)
 Triplets03 (2.1)6 (1.7)
Pregnancy induced hypertension, n (%)13 (37.1)69 (49.3)145 (40.1)
 Missing001
Absent/reversed doppler abnormality, n(%)35 (100.0)138 (98.6)347 (95.6)
Given antenatal steroids, n (%)34 (97.1)132 (95.7)331 (91.4)
 Missing021
Onset of delivery, n (%)
 Spontaneous2 (5.7)2 (1.4)7 (1.9)
 Induced01 (0.7)4 (1.1)
 Caesarean33 (94.3)137 (97.9)352 (97.0)
Apgar score at 5 min
 Median (IQR)9 (8 to 9)9 (8 to 10)9 (9 to 10)
 Missing227
Ventilated at trial entry, n (%)2 (5.7)30 (21.4)45 (12.4)
CPAPb at trial entry, n (%)22 (62.9)78 (55.7)122 (33.6)
UACc in situ at trial entry, n (%)11 (31.4)35 (25.0)44 (12.1)
UVCd in situ at trial entry, n (%)19 (54.3)67 (48.6)92 (25.4)
 Missing021
Any diagnosis of severe NECe35 (100.0)8 (5.7)0
  1. a109 unique controls. Each case is matched to 4 controls with the same sex and the smallest distance in terms of the Mahalanobis distance based on gestational age and birth weight. For cases where the difference is the same, infants are selected at random. bContinuous Positive Airway Pressure. cUmbilical artery catheter. dUmbilical venous catheter. eMatched controls can include infants who develop severe necrotising enterocolitis at some time in the future