Table 3

Descriptive statistics for the sample of preterm infants born ≤32⁺⁶ weeks gestation by designation of the neonatal unit nearest to maternal place of residence

	Unit level designation				Unit volume*
	Nearest unit tertiary level	Nearest unit non-tertiary level	p Value†	p Value‡, controlling for deprivation	Nearest unit high volume	Nearest unit non-high volume	p Value†	p Value‡, controlling for deprivation
n (%)	7167 (34.9)	13 387 (65.1)			7357 (35.8)	13 197 (64.2)
Gestation (weeks), mean (SD)	29.6 (2.4)	29.7 (2.3)	0.040	0.418	29.6 (2.4)	29.6 (2.3)	0.181	0.526
Birth weight (g), mean (SD)	1377.4 (429.2)	1394.2 (424.5)	0.007	0.262	1376.7 (426.7)	1394.8 (425.7)	0.004	0.111
Received full or partial course of antenatal steroids	4703 (65.6)	8953 (66.9)	0.069	0.584	4749 (64.6)	8907 (67.5)	<0.001	0.052
Deprivation score bottom 10%	1751 (24.4)	1611 (12.0)	<0.001	NA	1476 (20.1)	1886 (14.3)	<0.001	NA
Male	3820 (53.3)	7165 (53.5)	0.761	0.854	3958 (53.8)	7027 (53.3)	0.447	0.378
Birth in hospital with tertiary-level unit	4753 (88.4)	2290 (22.5)	<0.001	<0.001	3839 (69.5)	3204 (31.9)	<0.001	<0.001
Birth in hospital with high-volume unit	3703 (68.9)	3374 (33.1)	<0.001	<0.001	4764 (86.3)	2313 (23.0)	<0.001	<0.001

All values are n (%) and are a proportion of the column total unless otherwise stated.
*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.
†Continuous variables were tested by t test, categorical variables by χ² test.
‡p Value of F-test of coefficient on instrument from a regression of variable of interest on instrument and deprivation indicator.