Authors Location Date Type Pollutants
measured		 Number of
cases		 Outcomesa Conclusion
Ritz et al. [12] California, USA 1987 - 1993 Case/
control 		CO, O3 CP: 189
CL/P: 450 		CP and CO (3rd month):
OR = 0.71; 95% CI: 0.52 - 0.95 		Inconclusive for orofacial clefts
Chung et al. [17] Hong Kong 2002 - 2009 Case/
control 		NOx, O3, SO2 CP: 12
CL/P: 47 		CL and NOx: -0.9 (P = 0.018) CL/P and NO: -0.699 (P = 0.031) Protective effect of NOx
on CL and NO on CL/P
Dolk et al. [18] England 1991 - 1999 Cohort NO2, PM10, SO2 CP: 302
CL/P: 586 		None No consistent conclusions
Gilboa et al. [19] Texas, USA 1997 - 2000 Case/
control 		CO, NO2, O3, SO2, PM10 CP: 106
CL/P: 293 		CL/P and PM10 (23.8 - <29 mcg/m3):
OR = 1.45; 95% CI: 1.01 - 2.07 		Limited risk of orofacial clefts from air pollutants
Hansen et al. [20] Australia 1998 - 2004 Case/
control 		CO, NO2, O3, PM10, SO2 CP: 100
CL/P: 145 		CL/P and SO2:
OR = 1.27; 95% CI: 1.01 - 1.62
CP and PM10:
OR = 0.69; 95% CI: 0.5 - 0.93
CL/P and CO:
OR = 0.59; 95% CI: 0.42 - 0.8 		SO2 increases risk of CL/P;
PM10 protects against CP;
CO protects against CL/P
Hwang et al.
[21] 		Taiwan 2001 - 2003 Case/
control 		CO, NOx, O3, PM10, SO2 CL/P: 653 CL/P and O3 (16.6 ppb - 45.1 ppb):
1st month: OR = 1.2; 95% CI: 1.02 - 1.39
2nd month:
OR = 1.25; 95% CI: 1.03 - 1.52
Three-pollution model:
1st month:
OR = 1.18 - 1.2; 95% CI: 1.01 - 1.41 2nd month:
OR = 1.21 - 1.25; 95% CI: 1.03 - 1.56 		Increased risk of CL/P
with O3 exposure
Marshall et al. [22] New Jersey, USA 1998 - 2003 Case/
control 		CO, NO2, O3, PM10, SO2 CP: 303
CL/P: 414 		CL/P and SO2 (>0.007 ppm):
OR = 1.6; 95% CI: 1.1 - 2.2 CP and CO (>1.02 ppm):
OR = 0.5; 95% CI: 0.3 - 0.7 		Increased risk of CL/P with SO2 exposure;
Protective effect of CO on CP
Rankin et al. [23] England 1985 - 1990 Case/
control 		PM4, SO2 CL/P: 215 None Limited power of study with many confounders

aOnly statistically significant outcomes are included.