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4. Survival of infants born at periviable gestational ages;Patel;Clin Perinatol,2017
5. HCUP Sample Design: National Databases - Accessible Version.https://www.hcup-us.ahrq.gov/tech_assist/sampledesign/508_compliance/index508_2018.jsp#nisprior. Accessed 29 November 2021.