SCOPE Study:  Smoking and premature birth

Lesley McCowan

One of the first publications from the SCOPE study has found that women who stop smoking before week 15 of pregnancy reduce their risk of spontaneous premature birth and having small babies to the same as non-smokers. Women who do not quit by 15 week are three times more likely to give birth prematurely and twice as likely to have small babies compared to women who have stopped smoking. This finding demonstrates how important it is for women to give up smoking before 15 weeks of pregnancy, and to aim to become smoke free as early in pregnancy as possible.

While it is well established that smoking in pregnancy increases the risk of miscarriage, ectopic pregnancy, premature birth, small babies, stillbirth and neonatal death, no study has yet determined whether stopping smoking in early pregnancy reduces the risks of small babies and premature births.

Lesley McCowan and Robyn North and their team surveyed over 2,500 pregnant women participating in the SCOPE study in Australia and New Zealand at 15 weeks gestation. The participants were divided into three groups: non smoker, stopped smoker and current smoker. The ‘stopped smoker’ group all gave up before 15 weeks of pregnancy and 94% had stopped smoking by 12 weeks.

The results show that there were no differences between the rates of premature birth between stopped smokers and non-smokers, whereas women who continued to smoke at 15 weeks of pregnancy had a 3 fold higher risk. Similar results were revealed for expected baby size.

Another important finding was that women who stopped smoking were not more stressed than women who continued to smoke. The smoking status of the participants was also associated with social and health inequalities. Smokers were more likely to be single mothers, less well educated, unemployed, overweight or underweight. They were more likely to be drinking alcohol and less likely to be taking folic acid at 15 weeks of pregnancy.

These early findings from the SCOPE Study are of considerable public health importance. The data suggest that the adverse effect of smoking on late pregnancy outcomes may be largely preventable if smoking is stopped early in pregnancy. This gives pregnant women who smoke an important incentive to become smoke-free early in pregnancy.

Published March 2009 BMJ.com

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