Background Smoking in pregnancy is a public health challenge. Nicotine replacement therapy (NRT) is effective outside pregnancy, but because women metabolise nicotine and cotinine faster in pregnancy, it is unclear whether this will be effective for smoking cessation in pregnancy.

Methods The SNAP trial was designed to test the hypothesis that, in moderate and heavy pregnant smokers (>5/day), the addition of NRT transdermal patches (15 mg/16 h) for up to 8 weeks, to conventional behavioural advice, reduces the rate of smoking between the agreed quit date and delivery.

1051 pregnant smokers were recruited from seven centres up to February 2010. They were randomly allocated to either active or placebo patches. Both groups received standard behavioural advice.

The last recruit delivered in August 2010.

Results The main analyses and results will be complete by March 2010 and will be presented.

Discussion The implications of the results will be presented.

The trial is funded by the NHS HTA trials programme. ISRCTN07249128. Protocol available here: http://www.biomedcentral.com/1472-6963/7/2.