title: Spontaneous preterm birth and small for gestational age infants in women who stop smoking early in pregnancy: prospective cohort study.
abstract: OBJECTIVE
  To compare pregnancy outcomes between women who stopped smoking in early pregnancy and those who either did not smoke in pregnancy or continued to smoke.
  
  
  METHODS
  Prospective cohort study.
  
  
  METHODS
  Auckland, New Zealand and Adelaide, Australia.
  
  
  METHODS
  2504 nulliparous women participating in the Screening for Pregnancy Endpoints (SCOPE) study grouped by maternal smoking status at 15 (+/-1) week's gestation.
  
  
  METHODS
  Spontaneous preterm birth and small for gestational age infants (birth weight <10th customised centile). We compared odds of these outcomes between stopped smokers and non-smokers, and between current smokers and stopped smokers, using logistic regression, adjusting for demographic and clinical risk factors.
  
  
  RESULTS
  80% (n=1992) of women were non-smokers, 10% (n=261) had stopped smoking, and 10% (n=251) were current smokers. We noted no differences in rates of spontaneous preterm birth (4%, n=88 v 4%, n=10; adjusted odds ratio 1.03, 95% confidence interval l0.49 to 2.18; P=0.66) or small for gestational age infants (10%, n=195 v 10%, n=27; 1.06, 0.67 to 1.68; P=0.8) between non-smokers and stopped smokers. Current smokers had higher rates of spontaneous preterm birth (10%, n=25 v 4%, n=10; 3.21, 1.42 to 7.23; P=0.006) and small for gestational age infants (17%, n=42 v 10%, n=27; 1.76, 1.03 to 3.02; P=0.03) than stopped smokers.
  
  
  CONCLUSIONS
  In women who stopped smoking before 15 weeks' gestation, rates of spontaneous preterm birth and small for gestational age infants did not differ from those in non-smokers, indicating that these severe adverse effects of smoking may be reversible if smoking is stopped early in pregnancy.
authors.affiliation: Department of Obstetrics and Gynaecology, Faculty of Medical and Health Sciences, School of Population Health, University of Auckland, Auckland, New Zealand. l.mccowan@auckland.ac.nz
authors.forename: Lesley M E
authors.initials: LM
authors.lastname: McCowan
authors.forename: Gustaaf A
authors.initials: GA
authors.lastname: Dekker
authors.forename: Eliza
authors.initials: E
authors.lastname: Chan
authors.forename: Alistair
authors.initials: A
authors.lastname: Stewart
authors.forename: Lucy C
authors.initials: LC
authors.lastname: Chappell
authors.forename: Misty
authors.initials: M
authors.lastname: Hunter
authors.forename: Rona
authors.initials: R
authors.lastname: Moss-Morris
authors.forename: Robyn A
authors.initials: RA
authors.lastname: North