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Table 1 Sub-categories of preterm birth, based on gestational age. From WHO. Preterm birth. Fact sheet. 2016. www.who.int/mediacentre/factsheets/fs363/en/. (modified)

From: Hexavalent vaccines in preterm infants: an update by Italian Society of Pediatric Allergy and Immunology jointly with the Italian Society of Neonatology

Subcategory of preterm birth

Gestational age

moderate to late preterm

32 to 37 weeks

very preterm

28 to 32 weeks

extremely preterm

<  28 weeks

  1. Preterm is defined as babies born alive before 37 weeks of pregnancy are completed