The intervention group received routine care plus the offer of up to 400 of shopping vouchers : 50 for attending a face to face appointment and setting a quit date ; then another 50 if at four weeks ' post-quit date exhaled carbon monoxide confirmed quitting ; a further 100 was provided for continued validated abstinence of exhaled carbon monoxide after 12 weeks ; a final 200 voucher was provided for validated abstinence of exhaled carbon monoxide at 34-38 weeks ' gestation .