Table 3

Study characteristics and outcomes for studies characterising neonates by gestational age and birth weight

Categorisation method	Type of study (comparator groups)	Study	Country of study	Total number of babies	Population (gestation (weeks ^+days)/birth weight (g))	Outcomes reported by included studies
						Mortality timeframe						Survival timeframe		Morbidity
						Undefined	Perinatal	Neonatal	Discharge	Infant	2 years	Discharge	2 years	Morbidity
Gestational age	Inutero versus exutero transfer to NICU	Lamont et al28	UK	206	28⁺⁰–29⁺⁶									Non-significant difference in incidence of IVH.
		Lamont et al28	UK	206	30⁺⁰–31⁺⁶							NS		Significant reduction in incidence of IVH.
		Truffert et al31	France	157	27⁺⁰–30⁺⁶						NS			Non-significant difference in incidence of survival (up to 2 years of age) without disability.*
		Hauspy et al32	Belgium	315	28⁺⁰–29⁺⁶			NS						Non-significant difference in incidence of RDS.
		Hauspy et al32	Belgium	315	30⁺⁰–31⁺⁶			NS						Non-significant difference in incidence of RDS.
		Lee et al33	Canada	2148	27⁺⁰–29⁺⁶				NS					Non-significant difference in incidence of IVH, NEC and ROP. Significant reduction in incidence of RDS and CLD.
		Lee et al33	Canada	2148	30⁺⁰–31⁺⁶				NS					Non-significant difference in incidence of IVH, NEC, ROP and CLD. Significant reduction in incidence of RDS.
		Boland et al13	Australia	250	28⁺⁰–31⁺⁶									No other outcomes measured.
	Level of unit of birth (NICU vs non-NICU)	Holmgren and Högberg 34	Sweden	394	28⁺⁰–31⁺⁶		NS	NS		NS				Non-significant difference in incidence of asphyxia†
	Level of unit of birth (NICU vs non-NICU)	Johansson et al29	Sweden	1636	28⁺⁰–31⁺⁶					NS				No other outcomes measured.
	Level of unit of care (NICU vs non-NICU)	Field et al30	UK	171	29⁺⁰–30⁺⁶	NS								No other outcomes measured.
	Level of unit of care (NICU vs non-NICU)	Jonas and Lumley35	Australia	3331	28⁺⁰–31⁺⁶									No other outcomes measured.
Birth weight	Inutero versus exutero transfer to NICU	Miller et al38	USA	94	1000–1500									No other outcomes measured.
		Watkinson and McIntosh44	UK	154	1001–1500									No other outcomes measured.
		Powell and Pharoah42	UK	390	1000–1500									No other outcomes measured.
		Obladen et al40	Germany	220	1000–1249							NS		Non-significant difference in incidence of IVH.
		Obladen et al40	Germany	220	1250–1499							NS		No other outcomes measured.
		Mohamed and Aly39	USA	36 493	1000–1500									Significant reduction in incidence of IVH.
	Level of unit of birth (NICU vs non-NICU)	Gortmaker et al36	USA	4874	1000–1500									No other outcomes measured.
		Powell et al41	USA	947	1000–1500					NS				No other outcomes measured.
		Yeast et al1	USA	2852	1000–1500									No other outcomes measured.
		Sanderson et al43	USA	1345	1000–1249									No other outcomes measured.
		Sanderson et al43	USA	1345	1250–1499			NS						No other outcomes measured.
		Gould et al37	USA	undefined (<4405)	1000–1500			NS						No other outcomes measured.
		Warner et al18	USA	474	1000–1500				NS					Non-significant difference in incidence of NEC (Bell stage II or III) or death. Significant reduction in incidence of BPD or death, IVH (grade III or IV) or death, ROP or death.

↑denotes direction of significant difference found between comparator groups (first comparator vs second comparator), and NS denotes lack of significant difference between comparator groups). For example, Jonas 1997 showed a significantly lower (arrow in downward direction) neonatal mortality for those babies born between 28⁺⁰ and 31⁺⁶ in a NICU (first comparator) versus a non-NICU (second comparator).
*Disability is a composite outcome measure consisting of cerebral palsy, deafness, Brunet-Lézine developmental score <80.63
†Asphyxia refers to Apgar score <5 at 10 min of age.
BPD, bronchopulmonary dysplasia; CLD, chronic lung disease; IVH, intraventricular haemorrhage; NEC, necrotising enterocolitis; NICU, neonatal intensive care unit; RDS, respiratory distress syndrome; ROP, retinopathy of prematurity.