title: Previous abortion and risk of pre-term birth: a population study.
abstract: OBJECTIVE
  This population study was undertaken to determine whether previous abortion is an independent risk factor for pre-term birth and to calculate population-attributable risks for risk factors.
  
  
  METHODS
  All South Australian first singleton births in 1998-2003 (n = 42 269) were included in a multivariable logistic regression analysis, comparing pre-term births with term births.
  
  
  RESULTS
  Risk factors for pre-term birth were found to be: being indigenous, single, a smoker [adjusted odds ratio (AOR) 1.28, 95% confidence interval 1.17-1.41], age 40 years or older, reproductive technology assistance, threatened miscarriage, antepartum haemorrhage, urinary tract infection, pregnancy hypertension and suspected intra-uterine growth restriction. A previous spontaneous abortion was of borderline statistical significance, whereas a previous induced abortion (AOR 1.25, 1.13-1.40) was an independent risk factor. A dose-response relationship was found with increasing number of previous spontaneous or induced abortions. Population-attributable risks were highest for pregnancy hypertension (12.4%) and antepartum haemorrhage (9.2%). Smoking and previous induced abortion had risks of 4.7% and 2.7%, respectively. Among indigenous women, 51% of whom smoked, 16.4% of pre-term birth could be attributed to smoking.
  
  
  CONCLUSIONS
  A previous induced abortion and smoking during pregnancy (particularly among indigenous women) are preventable risk factors for pre-term birth. Their population-attributable risks are likely to be under-estimates from under-reporting.
authors.affiliation: Discipline of Public Health, University of Adelaide, South Australia, Australia.
authors.forename: Rosanne
authors.initials: R
authors.lastname: Freak-Poli
authors.forename: Annabelle
authors.initials: A
authors.lastname: Chan
authors.forename: Graeme
authors.initials: G
authors.lastname: Tucker
authors.forename: Jackie
authors.initials: J
authors.lastname: Street
mesh_terms: D000028:Abortion, Induced / Q000009:adverse effects* / Q000706:statistics & numerical data*; D000328:Adult; D001315:Australia / Q000453:epidemiology; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D016017:Odds Ratio; D011153:Population; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology; D047928:Premature Birth / Q000453:epidemiology* / Q000209:etiology*; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects / Q000453:epidemiology; D055815:Young Adult