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Method

For current guidelines, we performed online searches using Google and the keywords" smoking cessation"," guidelines" and" name of country". We included national guidelines from high income countries (eg, Australia, UK, US, Canada and New Zealand) published in English from the year 2010 onward.

We conducted MEDLINE searches on NRT safety, efficacy and effectiveness, using the Medical Subject Headings and keywords" nicotine"," nicotine replacement therapy"," fetal" and" pregnancy"-limited to the English language with no limit on the years. Previous reviews were manually searched to identify further studies. We included both observational and interventional studies that aimed to specifically assess either the safety or efficacy of NRT during pregnancy. Studies that included NRT as part of a multicomponent intervention were excluded, as their design does not permit determining the effect of NRT alone.