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