Comorbidity	EP Infants (≤28 wGA) (n=4462)	VP Infants (>28 to <32 wGA) (n=2904)	M-LP Infants (≥32 to <37 wGA) (n=18 207)
Cardiovascular
PDA	2103 (47.1)	555 (19.1)	823 (4.5)
Gastrointestinal
NECa	463 (10.4)	128 (4.4)	239 (1.3)
Stage 1	28 (0.6)	11 (0.4)	18 (0.1)
Stage 2	44 (1.0)	18 (0.6)	30 (0.2)
Stage 3	61 (1.4)	7 (0.2)	9 (0.05)
Unspecified stage	137 (3.1)	26 (0.9)	66 (0.4)
Spontaneous intestinal perforation	97 (2.2)	11 (0.4)	32 (0.2)
Neurologicalb
IVH	1121 (25.1)	416 (14.3)	593 (3.3)
Stage 1	344 (7.7)	244 (8.4)	373 (2.0)
Stage 2	226 (5.1)	56 (1.9)	58 (0.3)
Stage 3	159 (3.6)	39 (1.3)	38 (0.2)
Stage 4	224 (5.0)	24 (0.8)	17 (0.1)
Unspecified stage	159 (3.6)	51 (1.8)	104 (0.6)
Intracerebral hemorrhage	493 (11.0)	138 (4.8)	451 (2.5)
General neurological dysfunction	287 (6.4)	107 (3.7)	396 (2.2)
PVL	168 (3.8)	53 (1.8)	45 (0.2)
Cerebral palsy	3 (0.1)	0 (0)	4 (0.02)
Ophthalmological
ROP	996 (22.3)	297 (10.2)	383 (2.1)
Stage 1	286 (6.4)	67 (2.3)	18 (0.1)
Stage 2	290 (6.5)	35 (1.2)	12 (0.1)
Stage 3	174 (3.9)	12 (0.4)	9 (0.05)
Stage 4	2 (0.04)	0 (0.0)	0 (0.0)
Stage 5	2 (0.04)	0 (0.0)	0 (0.0)
Unspecified stage	242 (5.4)	183 (6.3)	344 (1.9)
Retinal detachment	30 (0.7)	0 (0.0)	0 (0.0)
Other
BPD	2256 (50.6)	418 (14.4)	437 (2.4)
Acute RDS	4082 (91.5)	2384 (82.1)	8242 (45.3)
Bacterial sepsis	180 (4.0)	67 (2.3)	166 (0.9)
Hearing loss	41 (0.9)	23 (0.8)	121 (0.7)
Bacterial meningitis	40 (0.9)	5 (0.2)	11 (0.1)
Medical procedures
Intubation for BPD/RDS	2413 (54.1)	1115 (38.4)	2823 (15.5)
Ligation for PDA	406 (9.1)	22 (0.8)	9 (0.05)
Laser surgery/cryotherapy for ROP	110 (2.5)	2 (0.1)	1 (0.005)
Bowel surgery for NEC	92 (2.1)	15 (0.5)	29 (0.2)
Hydrocephalus shunting for IVH	107 (2.4)	21 (0.7)	14 (0.1)
Tracheostomy for BPD/RDS	28 (0.6)	1 (0.03)	12 (0.1)