“…Cigarette smoke exposure, along with alcohol (Romitti et al, 2007) and nutrition (Yazdy et al, 2007) are the most studied environmental factors in the causes of oral clefts. Positive association between maternal cigarette smoking and CL/P or CPO in their offspring have been reported in several studies (Khoury et al, 1987(Khoury et al, , 1989Beaty et al, 1997;Kallen, 1997a;Wyszynski et al, 1997;Chung et al, 2000;Wyszynski and Wu, 2002); nevertheless, this association failed to be confirmed in some other studies (Werler et al, 1990;Christensen et al, 1999;Lieff, 1999;Mitchell et al, 2001). Little et al (2004) performed a meta-analysis of the association between maternal smoking during pregnancy and oral clefts using data from 24 case-control and cohort studies.…”