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Spontaneous preterm birth and small for gestational age infants in women who stop smoking early in pregnancy: prospective cohort study

BMJ 2009; 338 doi: (Published 27 March 2009) Cite this as: BMJ 2009;338:b1081

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  1. Lesley M E McCowan, associate professor of obstetrics and gynaecology1,
  2. Gustaaf A Dekker, professor of obstetrics and gynaecology6,
  3. Eliza Chan, research fellow1,
  4. Alistair Stewart, statistician2,
  5. Lucy C Chappell, senior lecturer in maternal and fetal medicine4,
  6. Misty Hunter, medical student1,
  7. Rona Moss-Morris, professor of health psychology5,
  8. Robyn A North, professor in obstetric medicine3
  9. On behalf of the SCOPE consortium
  1. 1Department of Obstetrics and Gynaecology, Faculty of Medical and Health Sciences, School of Population Health, University of Auckland, Auckland, New Zealand
  2. 2Department of Epidemiology and Biostatistics, Faculty of Medical and Health Sciences, School of Population Health, University of Auckland, Auckland, New Zealand
  3. 3Discipline of Obstetrics and Gynaecology, School of Paediatrics and Reproductive Health, University of Adelaide, Australia
  4. 4Division of Reproduction and Endocrinology, King’s College London
  5. 5School of Psychology, University of Southampton
  6. 6Women and Children’s Division, Lyell McEwin Hospital, University of Adelaide, Adelaide, South Australia
  1. Correspondence to: L M E McCowan, Department of Obstetrics and Gynaecology l.mccowan{at}
  • Accepted 1 March 2009


Objectives 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.

Design Prospective cohort study.

Setting Auckland, New Zealand and Adelaide, Australia.

Participants 2504 nulliparous women participating in the Screening for Pregnancy Endpoints (SCOPE) study grouped by maternal smoking status at 15 (±1) week’s gestation.

Main outcome measures 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.

Conclusion 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.


  • Acknowledgments: We thank the pregnant women who participated in the SCOPE study, Claire Roberts for her contributions in establishing the SCOPE study in Adelaide, Rennae Taylor for coordinating the New Zealand SCOPE study and assistance with manuscript preparation, Denise Healy for coordinating the Australian SCOPE study, the SCOPE research midwives, and Hayden McRobbie for helpful comments on the manuscript.

  • Contributors: LMEMcC is guarantor. LMEMcC, GAD, LCC, MH, RAN, and RMM had a role in conception and design. LMEMcC, GAD, EC, AS, LCC, RAN, and RMM interpreted data. All authors took part in drafting the article or revising it for critically important intellectual content and all gave final approval of the version to be published.

  • Funding: New Zealand SCOPE Study—New Enterprise Research Fund, Foundation for Research Science and Technology; Health Research Council; Evelyn Bond Fund, Auckland District Health Board Charitable Trust. Australian SCOPE Study—Premier’s Science and Research Fund, South Australian Government. The study sponsors had no role in study design, data analysis, or writing this report.

  • Competing interests: None declared.

  • Ethical approval: Ethical approval was gained from local ethics committees (New Zealand AKX/02/00/364 and Australia REC 1712/5/2008) and all women provided written informed consent.

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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