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Subgroup analysis of different exposure time windows and stillbirth.
| Subgroup | No. study | Pooled RR (95% CI) | I2 (%) |
| Preconception | 1 | 1.21 (0.97, 1.50) | – |
| First trimester | 2 | 1.02 (0.80, 1.29) | 40 |
| Second trimester | 2 | 1.08 (0.80, 1.46) | 70 |
| Third trimester | 1 | 1.53 (0.83, 2.82) | – |
| A week before delivery | 2 | 1.05 (0.98, 1.12) | 49 |
| Entire pregnancy | 2 | 4.63 (3.99, 5.38) | 0 |
CI: Confidence interval; RR: Risk ratio.
