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A Closer Look: Q&A with Tim Nawrot

Time NawrotTim Nawrot is a scientist at Belgium’s Hasselt University.   He led a research team that investigated trends in preterm births, those occurring before 37 weeks gestation, from 2002 to 2011 covering a period before, during and after the introduction of smoke-free laws in Belgium.  The study shows a consistent pattern of reduction in the risk of preterm delivery as successive interventions to restrict smoking in public spaces were implemented in Belgium.

Can you summarize what is known about maternal exposure to cigarette smoke and birth/health outcomes for the baby?

It is well-established that active maternal smoking during pregnancy impairs fetal growth and shortens gestation.  Secondhand smoke has also been found to affect birth outcomes.  Exposure of non-smoking pregnant women to secondhand smoke has been estimated to increase the risk of lower birth weight, and many studies report a significant association between secondhand smoke and premature birth.  Despite this growing evidence that secondhand smoke has a negative impact on pregnancy duration and birth weight, few studies have shown a beneficial impact of smoke-free legislation on pregnancy outcomes.

Your study showed a consistent pattern of reduction in the risk of preterm delivery with public regulation to restrict smoking in all public places and workspaces in Flanders, Belgium.  How significant was the reduction? 

Stepwise implementation of smoke-free legislation in Belgium allowed the demonstration of suc
cessive reductions in preterm deliveries which persisted after the implementation of the different legislation phases. The largest reductions in preterm birth coincided with the implementation of the second and the third phase of the legislation (smoking ban in restaurants and in bars serving food, respectively).  In total, the risk decreased by about 6% over the three different smoking bans. Even a small relative decline in preterm deliveries can have important public health benefits as preterm birth has health consequences later in life.  The main limitation to our study, common to studies on smoking bans, is that we do not have data on individual smoking status. The birth records also did not allow us to address other known risk factors for preterm birth, such as marital status, psychosocial stressors, maternal weight, occupation, and nutrition.

Have similar studies been done and, if so, how do the results compare?

A similar study has been conducted in Scotland. The smoking ban was implemented fully at one moment and a reduction in the risk of preterm birth by 11% was observed. Another study on maternal smoking status assessed by measuring nicotine in hair found an increase of approximately 20% in preterm birth risk per 1 µg/g increase in nicotine use/exposure.

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