Table 1.
Meta-analysis results by outcome and temperature metric
| No of studies | Synthesis method | No of studies in summary measure | Average effect size (OR (95% CI)) |
I2 (%) | |
|---|---|---|---|---|---|
| Preterm birth: | |||||
| Odds of preterm birth during heatwaves | 6 | Meta-analysis | 6 | 1.16 (1.10 to 1.23) | 44.7 |
| Odds of preterm birth per 1°C temperature increase | 6 | Meta-analysis | 6 | 1.05 (1.03 to 1.07); 5% increase per 1°C rise (3% to 7%) | 87.7 |
| Odds of preterm birth during high versus low temperatures (exposure over a trimester or all of pregnancy) | 9 | Meta-analysis | 9 | 1.14 (1.11 to 1.16) | 88.2 |
| 8* | 1.15 (1.13 to 1.18) | 65.2 | |||
| Odds of preterm birth during high versus low temperatures with exposure period <4 weeks | 21 | Meta-analysis | 21 | 1.01 (1.01 to 1.02) | 89.8 |
| 19† | 1.05 (1.04 to 1.05) | 83.6 | |||
| 21 | Summary of effect estimates | 21 | Median OR=1.07 (IQR 1.05-1.16; range 0.99-1.94) | — | |
| Birth weight: | |||||
| Odds of low birth weight during high versus low temperatures (exposure over a trimester or all of pregnancy) | 9 | Summary of effect estimates | 8‡ | Median OR 1.09 (IQR 1.04-1.47; range 1.01-2.49) | — |
| Changes in birth weight at high versus low temperatures | 6 | Summary of effect estimates | 4§ | Median difference −25.5 g (range −39.4 to −15.0) | — |
| Stillbirth: | |||||
| Odds of stillbirth during heatwaves | 1 | — | 1 | 1.46 (1.09 to 1.96) | — |
| Odds of stillbirth per 1°C temperature increase | 3 | Meta-analysis | 3 | 1.05 (1.01 to 1.08) | 81.3 |
| Odds of stillbirth during high versus low temperatures (exposure over a trimester or all of pregnancy) | 2 | Meta-analysis | 2 | 3.39 (2.33 to 4.96) | 27.8 |
| Odds of stillbirth during high versus low temperatures with exposure period <1 week | 4 | Meta-analysis | 4 | 1.24 (1.12 to 1.36) | 53.1 |