Included studies Air pollutant Type of
orofacial cleft
Number of cases Odds ratio 95% confidence
interval
P-valuea
Gilboa et al. [19]
Hansen et al. [20]
Hwang et al. [21]
Marshall et al. [22]
Rankin et al. [23]
CO CL/P 1,955 1 0.98 - 1.02 0.89
Ritz et al. [12]
Gilboa et al. [19]
Hansen et al. [20]
Marshall et al. [22]
CP 698 0.88 0.78 - 0.99 0.03
Dolk et al. [18]
Gilboa et al. [19]
Hansen et al. [20]
Hwang et al. [21]
Marshall et al. [22]
NOx CL/P 2,138 0.98 0.91 - 1.06 0.66
Dolk et al. [18]
Gilboa et al. [19]
Hansen et al. [20]
Marshall et al. [22]
CP 823 0.84 0.71 - 1 0.04
Ritz et al. [12]
Gilboa et al. [19]
Hansen et al. [20]
Hwang et al. [21]
O3 CL/P 1,955 1.08 1.01 - 1.16 0.02
Ritz et al. [12]
Gilboa et al. [19]
Hansen et al. [20]
Marshall et al. [22]
CP 698 1.08 0.95 - 1.22 0.23
Dolk et al. [18]
Gilboa et al. [19]
Hansen et al. [20]
Hwang et al. [21]
Marshall et al. [22]
PM10 CL/P 2,091 1 0.98 - 1.03 0.76
Dolk et al. [18]
Gilboa et al. [19]
Hansen et al. [20]
Marshall et al. [22]
CP 811 1.02 0.88 - 1.19 0.78
Dolk et al. [18]
Gilboa et al. [19]
Hansen et al. [20]
Hwang et al. [21]
Marshall et al. [22]
Rankin et al. [23]
SO2 CL/P 2,306 1.02 0.92 - 1.11 0.75
Dolk et al. [18]
Gilboa et al. [19]
Hansen et al. [20]
Marshall et al. [22]
CP 811 0.99 0.88 - 1.13 0.91

aMeta-analysis was performed using a fixed effects model with inverse variance, with P < 0.05 considered statistically significant.