title: Previous miscarriage and the subsequent risk of preterm birth in Scotland, 1980-2008: a historical cohort study.
abstract: OBJECTIVE
  To determine whether the relationship between previous miscarriage and risk of preterm birth changed over the period 1980-2008, and to determine whether the pattern varied according to the cause of the preterm birth.
  
  
  METHODS
  Linked birth databases.
  
  
  METHODS
  All Scottish NHS hospitals.
  
  
  METHODS
  A total of 732 719 nulliparous women with a first live birth between 1980 and 2008.
  
  
  METHODS
  Risk was estimated using logistic regression.
  
  
  METHODS
  Preterm birth, subdivided by cause (spontaneous, induced with a diagnosis of pre-eclampsia, or induced without a diagnosis of pre-eclampsia) and severity [extreme (24-28 weeks of gestation), moderate (29-32 weeks of gestation), and mild (33-36 weeks of gestation)].
  
  
  RESULTS
  Consistent with previous studies, previous miscarriage was associated with an increased risk of all-cause preterm birth (adjusted odds ratio, aOR 1.26; 95% confidence interval, 95% CI 1.22-1.29). This arose from associations with all subtypes. The strongest association was found with extreme preterm birth (aOR 1.73; 95% CI 1.57-1.90). Risk increased with the number of miscarriages. Women with three or more miscarriages had the greatest risk of all-cause preterm birth (aOR 2.14; 95% CI 1.93-2.38), and the strongest association was with extreme preterm birth (aOR 3.87; 95% CI 2.85-5.26). The strength of the association between miscarriage and preterm birth decreased from 1980 to 2008. This was because of weakening associations with spontaneous preterm birth and induced preterm birth without a diagnosis of pre-eclampsia.
  
  
  CONCLUSIONS
  The association between a prior history of miscarriage and the risk of preterm birth declined in Scotland over the period 1980-2008. We speculate that changes in the methods of managing incomplete termination of pregnancy might explain the trend, through reduced cervical damage.
authors.affiliation: Department of Public Health and Primary Care, University of Cambridge, Cambridge, UK.
authors.forename: C
authors.initials: C
authors.lastname: Oliver-Williams
authors.affiliation: Information Services Division, NHS National Services Scotland, Edinburgh, UK.
authors.forename: M
authors.initials: M
authors.lastname: Fleming
authors.affiliation: Department of Public Health and Primary Care, University of Cambridge, Cambridge, UK.
authors.forename: A M
authors.initials: AM
authors.lastname: Wood
authors.affiliation: Department of Obstetrics and Gynaecology, NIHR Biomedical Research Centre, University of Cambridge, Cambridge, UK.
authors.forename: Gcs
authors.initials: G
authors.lastname: Smith
mesh_terms: D000026:Abortion, Habitual / Q000453:epidemiology; D000022:Abortion, Spontaneous / Q000453:epidemiology*; D000328:Adult; D015331:Cohort Studies; D016208:Databases, Factual; D005260:Female; D006801:Humans; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D016016:Proportional Hazards Models; D012306:Risk; D012606:Scotland / Q000453:epidemiology; D055815:Young Adult
keywords: Miscarriage; premature birth; spontaneous termination of pregnancy