Researchers: Stopping smoking by 15th week of pregnancy

By Dr. Jai Ellis - email

It is a well known fact that smoking during pregnancy may lead to such ills as miscarriage, pre-eclampsia and still birth, but may also cause pre-term labor and low birth weight infants. In the late 1990s, it was estimated that in the US $1.9 billion were spent on health care for premature and low-birth weight infants. Much of this risk and expenditure is believed to be avoidable if smoking cessation could be achieved more readily. Nicotine is a stimulant which elevates blood pressure by constricting blood vessels and, therefore, there is a chronic decrease in oxygen delivery to all of the tissues in the body, of which the placenta is no exception. If the placenta does not receive adequate oxygenation, then the fetus will suffer a similar insult.

Obviously, prudent advice for the pregnant woman is that she not smoke during pregnancy. Very few women, however, are likely to abstain completely throughout the entirety of the pregnancy. Therefore, researchers at the University of Auckland in New Zealand have looked at the effects of smoking cessation at different gestational ages. The British Medical Journal has recently published an article which documents some of the research to date. This is the first study comparing the incidence of pre-term labor and low birth weight status in women whom have never smoked, women whom quit smoking during pregnancy and women whom continued to smoke throughout their pregnancy.

In a study of 2,504 women who had never before had children, 80% were non-smokers and were used as controls. 10% were smokers who quit prior to 15 weeks gestation; and the remaining 10% smoked for throughout the entire gestation. Women at risk for pre-eclampsia, pre-term labor, or whom had had 3 or more previous miscarriages or terminations were excluded from the study. Because other studies have indicated that stress, anxiety and depression may be risk factors for pre-term labor and low birth weight infancy, subjects were chosen whom all had the same stress, anxiety and depression scores by survey. The results showed that, not only did the risk of having pre-term labor or a low birth weight infant diminish when smoking was ceased by 15 weeks, but the risk returned to that of a woman with a non-smoking status! Specifically, for current smokers, the rate of pre-term labor was three times higher for smokers than non or stopped smokers. As for low birth weight infants, the rate was double in current smokers that of non and stopped smokers.

It was found that the average number of cigarettes smoked daily was higher in the group whom continued to smoke. They smoked an average of 17.8 cigarettes per day, while the smokers who quit smoked 8.9 daily.

One limitation of the study is that smoking assessment was made by patient self-reporting and was not confirmed by checking cotinine levels. The authors also found that women in the smoking group were more likely to come from disadvantaged socioeconomic groups, have less financial resources and less education. These can also be confounding variables when discussing pre-term labor and low birth weight infants.

Finally, there is no comment as to whether the participants used any smoking cessation aids that may have mimicked the effect of nicotine.

Based upon these findings, the authors of the study recommend that every effort is made to help women to stop smoking by 15 weeks of pregnancy. They do go on to say, however, that if the patient is still smoking by 16 weeks that efforts to stop smoking are not reduced or abandoned. The authors state unequivocally that some benefit may be derived in smoking cessation by as late as 32 weeks. This knowledge merely enables a pregnant woman to minimize risk to her fetus and optimize the infant's health.