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

Women who stop smoking before week 15 of pregnancy cut their risk of spontaneous premature birth and having small babies to the same as non-smokers, according to research published on bmj.com today.

Women who do not quit by 15 weeks, are three times more likely to give birth prematurely and twice as likely to have small babies compared to women who have stopped smoking, say the researchers. The lead author, Dr Lesley McCowan at the University of Auckland, says that maternity care providers need to emphasise to women the major benefits of giving up smoking before 15 weeks in pregnancy with the goal of becoming 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, say the authors, no study has yet determined whether stopping smoking in early pregnancy reduces the risks of small babies and premature births.

The authors 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.

The results show that there were no differences between the rates of premature birth between stopped smokers and non-smokers, whereas current smokers had much 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 also revealed 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.

In conclusion, the authors say that their “results are of considerable public health importance. The data suggest that the adverse effects of smoking on these late pregnancy outcomes may be largely reversible if smoking is ceased early in pregnancy, offering an important incentive for pregnant women who smoke to become smoke-free early in pregnancy.”

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BMJ-British Medical Journal