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. 2018 Dec 4;2(1):e000316. doi: 10.1136/bmjpo-2018-000316

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© Author(s) (or their employer(s)) 2018. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

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Flow chart describing selection and exclusion of cases and controls. First, NEC cases were identified, cleaned of any multiple registrations and excluded if they did not meet inclusion criteria. Then, controls were randomly selected for each NEC case. *Personal identify number. MBR, Medical Birth Register; NEC, necrotising enterocolitis; NPR, National Patient Register.