At the inclusion visit when the women are smoking, saliva cotinine is collected and determined. The first dose of nicotine is adapted according to the saliva cotinine when smoking to obtain approximately 100 % substitution. A second saliva cotinine determination is realized 2 weeks later and at the next visit nicotine's daily dose is determined according to this second saliva cotinine results for the whole duration of pregnancy. This dose-adaptation is necessary to avoid as far as possible under- and overdosing of nicotine.