title: The impact of inter-pregnancy interval on subsequent risk of preterm birth.
abstract: OBJECTIVE
  The aim of the study was to assess optimal time to conceive after previous delivery associated with smallest risk of preterm birth.
  
  
  METHODS
  We selected all women (n = 2723) with their first and second singleton delivery between the years 2004 and 2012. Inter-pregnancy interval was defined as that between live birth and subsequent conception. We performed logistic regression analyses to assess the risk of preterm birth adjusted for maternal age and body mass index.
  
  
  RESULTS
  Association between inter-pregnancy interval and the natural logarithm of the adjusted relative risk of preterm birth had a J-shaped curve with lowest risk at 15 months after last birth.
  
  
  CONCLUSIONS
  The optimal time to conceive after a previous delivery is 15 months, as longer or shorter interval are associated with increased risk of preterm birth. Women with short or long inter-pregnancy intervals were 1.6 times more likely to experience preterm birth.
authors.affiliation: a Division of Obstetrics and Gynecology, Department of Perinatology , University Medical Centre Ljubljana , Slovenia.
authors.forename: Vid
authors.initials: V
authors.lastname: Janša
authors.affiliation: b Department of Obstetrics and Gynecology , Kaplan Medical Center, Rehovot, Affiliated with the Hadassah-Hebrew University School of Medicine , Jerusalem , Israel.
authors.forename: Isaac
authors.initials: I
authors.lastname: Blickstein
authors.affiliation: a Division of Obstetrics and Gynecology, Department of Perinatology , University Medical Centre Ljubljana , Slovenia.
authors.forename: Miha
authors.initials: M
authors.lastname: Lučovnik
authors.affiliation: a Division of Obstetrics and Gynecology, Department of Perinatology , University Medical Centre Ljubljana , Slovenia.
authors.forename: Vesna
authors.initials: V
authors.lastname: Fabjan-Vodušek
authors.affiliation: a Division of Obstetrics and Gynecology, Department of Perinatology , University Medical Centre Ljubljana , Slovenia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Verdenik
authors.affiliation: a Division of Obstetrics and Gynecology, Department of Perinatology , University Medical Centre Ljubljana , Slovenia.
authors.forename: Nataša
authors.initials: N
authors.lastname: Tul
mesh_terms: D000328:Adult; D001721:Birth Intervals; D005260:Female; D006801:Humans; D016015:Logistic Models; D011247:Pregnancy; D047928:Premature Birth / Q000209:etiology*; D012189:Retrospective Studies; D012307:Risk Factors
keywords: Inter-pregnancy interval; preterm delivery; risk factors