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

(http://www.bmj.com/cgi/content/abstract/338/mar26_2/b1081) Spontaneous preterm birth and small for gestational age infants in women who stop smoking early in pregnancy: prospective cohort study

Lesley M E McCowan, associate professor of obstetrics and gynaecology¹, Gustaaf A Dekker, professor of obstetrics and gynaecology⁶, Eliza Chan, research fellow¹, Alistair Stewart, statistician², Lucy C Chappell, senior lecturer in maternal and fetal medicine⁴, Misty Hunter, medical student¹, Rona Moss-Morris, professor of health psychology⁵, Robyn A North, professor in obstetric medicine³, On behalf of the SCOPE consortium

¹ Department of Obstetrics and Gynaecology, Faculty of Medical and Health Sciences, School of Population Health, University of Auckland, Auckland, New Zealand, ² Department of Epidemiology and Biostatistics, Faculty of Medical and Health Sciences, School of Population Health, University of Auckland, Auckland, New Zealand, ³ Discipline of Obstetrics and Gynaecology, School of Paediatrics and Reproductive Health, University of Adelaide, Australia, ⁴ Division of Reproduction and Endocrinology, King’s College London, ⁵ School of Psychology, University of Southampton, ⁶ Women and Children’s Division, Lyell McEwin Hospital, University of Adelaide, Adelaide, South Australia

Correspondence to: L M E McCowan, Department of Obstetrics and Gynaecology l.mccowan@auckland.ac.nz

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> 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.

Conclusion and policy implications
Data from this large prospective cohort study of nulliparous women have shown that stopping smoking before 15 weeks’ gestation is associated with rates of spontaneous preterm birth and small for gestational age infants similar to those in women who do not smoke in pregnancy. Maternity care providers should strive to assist pregnant women who smoke to stop early in pregnancy, emphasising the major health benefits if they cease to smoke before 15 weeks’ gestation.

What is already known on this topic Smoking is the single most modifiable risk factor for adverse pregnancy outcomes in developed countries Stopping smoking in pregnancy increases birth weight and reduces rates of all preterm birth The gestation by which smoking must stop to reverse effects of smoking on spontaneous preterm births and small for gestational age infants is not known What this paper adds Stopping smoking early in pregnancy, before 15 weeks’ gestation, results in rates of spontaneous preterm births and small for gestational age infants similar to those in non-smokers Women who continue to smoke at 15 weeks’ gestation are more likely than those who stop smoking to have spontaneous preterm birth Pregnant women should be offered support and interventions to help them stop smoking early in pregnancy

Cite this as: BMJ 2009;338:b1081

© McCowan et al 2009
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Published 26 March 2009, doi:10.1136/bmj.b1081
Cite this as: BMJ 2009;338:b1081