| No. of study | Summary RR (95%CI) | I2 (%) | P* | P** |
---|---|---|---|---|---|
Exposed period | Â | Â | Â | Â | 0.113 |
 First trimester | 4 | 1.12(0.97, 1.31) | 86 | 0.127 | |
 During pregnancy | 9 | 1.72(1.04, 2.84) | 81 | 0.035 | |
Indication |  |  |  |  | < 0.001 |
 Analgesic or antitussive treatment | 2 | 1.03(0.94, 1.13) | 47 | 0.549 | |
 Opioid abuse/opioid abuse treatment | 9 | 2.09 (1.74, 2.52) | 0 | <  0.001 | |
 Not reported | 2 | 0.97 (0.87, 1.10) | 42 | 0.661 | |
Adjusted for confounders |  |  |  |  | < 0.001 |
 Yes | 5 | 1.06 (0.93, 1.20) | 82 | 0.364 | |
 No | 8 | 2.07 (1.60, 2.68) | 9 | <  0.001 | |
Risk of bias assessment |  |  |  |  | < 0.001 |
 Moderate | 2 | 1.00 (0.85, 1.16) | 74 | 0.955 | |
 Serious | 3 | 1.21 (0.90, 1.63) | 89 | 0.214 | |
 Critical | 8 | 2.07 (1.60, 2.68) | 9 | <  0.001 |