Table 1. Characteristics of children in the training and validation groups.

		Training group		Validation group		p value
		n= 485	%	n= 976	%
Neonatal characteristics
Gestational age (weeks)
	24-27 weeks	102	(21	220	22	0.57
	28-29 weeks	107	(22	229	24
	30-32 weeks	276	(57	527	54
Birth weight Z-score
	<-1 SD	96	(20)	217	(22)	0.41
	(-1 ; 0) SD	204	(42)	477	(43)
	> 0 SD	185	(38)	342	(35)
Female		215	(44)	439	(45)	0.83
Mean creatinine ( mg/dl)
	24-27 weeks	1.4	(0.7)	1.4	(0.7)	0.27
	28-29 weeks	0.8	(0.4)	0.8	(0.3)
	30-32 weeks	0.7	(0.4)	0.7	(0.3)
Number of creatinine assessment
	24-27 weeks	20	(17)	22	(18)	0.78
	28-29 weeks	11	(10)	11	(9)
	30-32 weeks	5	(6)	6	(7)
Sodium variation (meq/l)
	24-27 weeks	21	(11)	20	(10)	0.98
	28-29 weeks	14	(10)	14	(7)
	30-32 weeks	9	(6)	9	(6)
Patent ductus arteriosus		59	(12)	119	(12)	0.98
Catecholamine treatment		42	(9)	70	(7)	0.32
Nosocomial infection		123	(25)	280	(29)	0.18
Bronchodysplasia: oxygenotherapy
	No oxygen	269	(56)	491	(50)	0.09
	< 28 days	131	(27)	323	(33)
	28 days- 36 weeks of GA	58	(12)	118	(12)
	> 36 weeks of GA	27	(6)	44	(5)
Cerebral lesions		17	(4)	64	(7)	0.02
Neonatal surgery		46	(10)	86	(9)	0.67
Necrotizing enterocolitis		11	(2)	30	(3)	0.38
Neonatal outcome
	Death	35	(7)	82	(8)	0.43
	Alive	450	(93)	894	(92)
Outcome at 2 years		n= 396	(%)	n= 784	(%)
	Optimal outcome	269	(68)	550	(70)	0.31
	Non-optimal outcome	85	(22)	179	(23)
	Missing data	35	(9)	51	(7)
	Genetic anomalies	6	(2)	2	(3)
	death	1	(3)	2	(3)