Table 1.

PubMed search strategy.

No.	Search items
#1	((((((((((Factor, Risk [Title/Abstract]) OR Factors, Risk [Title/Abstract]) OR Risk Factor [Title/Abstract]) OR Factors [Title/Abstract]) OR Factor [Title/Abstract])) OR relationship [Title/Abstract])) OR “Risk Factors” [Mesh]))
#2	(((((((((((((((Infants, Premature[Title/Abstract]) OR Preterm Infant[Title/Abstract]) OR Premature Infant[Title/Abstract]) OR Preterm Infants[Title/Abstract]) OR Infant, Preterm[Title/Abstract]) OR Infants, Preterm[Title/Abstract]) OR Premature Infants[Title/Abstract]) OR Neonatal Prematurity[Title/Abstract]) OR Prematurity, Neonatal[Title/Abstract])) OR “Infant, Premature”[Mesh]) OR (((((((Neonates[Title/Abstract]) OR Infants, Newborn[Title/Abstract]) OR Newborn Infant[Title/Abstract]) OR Newborn Infants[Title/Abstract]) OR Newborns[Title/Abstract]) OR Newborn[Title/Abstract]) OR Neonate[Title/Abstract])) OR “Infant, Newborn”[Mesh]))
#3	((“Ductus Arteriosus, Patent”[Mesh]) OR (((((Patency of the Ductus Arteriosus[Title/Abstract]) OR Patent Ductus Arteriosus[Title/Abstract]) OR Patent Ductus Arteriosus Familial[Title/Abstract]) OR PDA[Title/Abstract]) OR ductus arteriosus[Title/Abstract])))
#4	#1 AND #2 AND #3

PDA, patent ductus arteriosus.