There are no established evidences as to the effectiveness in smoking pregnant women of nicotine patches in increasing birth weight, smoking abstinence during pregnancy and concerning the safety their for the fetus/newborn. Moreover, recent studies have shown that the metabolism of nicotine is speeded up in pregnant women suggesting that dose adaptation may be necessary in this population. The main aim of this study is to assess the effectiveness of nicotine patch comparatively to a placebo patch in pregnant women on birth weight and maternal smoking abstinence. The main secondary objective is the assessment of safety of these treatments for the fetus/newborn and for the mother.