. 2014 Jul 2;4(7):e004856. doi: 10.1136/bmjopen-2014-004856

Table 4.

Adjusted ORs for outcomes associated with admission to either tertiary or high-volume neonatal care at the hospital of birth using an instrumental variable logistic regression model

Outcome	Tertiary neonatal unit			High-volume neonatal unit†
	(1) ≤32⁺⁶ weeks	(2) ≤26⁺⁶ weeks	(3) 27⁺⁰–32⁺⁶ weeks	(4) ≤32⁺⁶ weeks	(5) ≤26⁺⁶ weeks	(6) 27⁺⁰–32⁺⁶ weeks
Neonatal mortality	0.87 (0.66 to 1.15)	1.01 (0.63 to 1.61)	0.82 (0.58 to 1.14)	0.70* (0.53 to 0.92)	0.54** (0.33 to 0.87)	0.80 (0.56 to 1.13)
Any in-hospital mortality	0.85 (0.68 to 1.06)	0.95 (0.62 to 1.44)	0.84 (0.64 to 1.10)	0.68** (0.54 to 0.85)	0.51** (0.33 to 0.79)	0.80 (0.60 to 1.07)
BPD	1.19 (0.95 to 1.49)	1.04 (0.66 to 1.64)	1.17 (0.91 to 1.51)	1.05 (0.85 to 1.29)	1.78** (1.12 to 2.81)	0.96 (0.75 to 1.22)
Treatment for ROP	1.91* (1.16 to 3.14)	1.57 (0.83 to 2.96)	2.17* (1.06 to 4.47)	1.02 (0.60 to 1.73)	0.58 (0.29 to 1.15)	1.84 (0.83 to 4.05)
Surgery for NEC	1.17 (0.72 to 1.90)	0.81 (0.40 to 1.66)	1.34 (0.76 to 2.38)	1.26 (0.76 to 2.07)	1.11 (0.54 to 2.28)	1.35 (0.75 to 2.43)
PMA at discharge >40⁺⁰ weeks	0.95 (0.73 to 1.22)	0.83 (0.60 to 1.13)	0.97 (0.72 to 1.31)	0.92 (0.72 to 1.17)	1.04 (0.78 to 1.40)	0.86 (0.67 to 1.14)

Values are ORs (95% CI).

Models are adjusted for gestational age, gestational age squared, birthweight z-score, use of antenatal steroids, gender, infant year of birth and deprivation.

*p<0.05, **p<0.01, ***p<0.001. †High volume was defined as being in the top quartile of units by number of care days provided to infants born at ≤32⁺⁶ weeks gestation.

BPD, bronchopulmonary dysplasia; NEC, necrotising enterocolitis; PMA, postmenstrual age; ROP, retinopathy of prematurity.