Summary of findings for the main comparison.
Antioxidant(s) compared to placebo or no treatment/standard treatment for female subfertility
| Antioxidant(s) compared to placebo or no treatment/standard treatment for female subfertility | ||||||
| Patient or population: subfertile women who had been referred to a fertility clinic and might or might not be undergoing assisted reproductive techniques Setting: fertility clinic Intervention: antioxidant(s) Comparison: placebo or no treatment/standard treatment | ||||||
| Outcomes | Anticipated absolute effects* (95% CI) | Relative effect (95% CI) | № of participants (studies) | Quality of the evidence (GRADE) | Comments | |
| Risk with placebo or no treatment/standard treatment | Risk with Antioxidant(s) | |||||
| Live birth; antioxidants vs placebo or no treatment/standard treatment (natural conceptions and undergoing fertility treatments) | 196 per 1,000 | 342 per 1,000 (262 to 433) | OR 2.13 (1.45 to 3.12) | 651 (8 RCTs) | ⊕⊝⊝⊝ VERY LOW 1, 2 | |
| Clinical pregnancy; antioxidants vs placebo or no treatment/standard treatment (natural conceptions and undergoing fertility treatments) | 220 per 1,000 | 301 per 1,000 (270 to 332) | OR 1.52 (1.31 to 1.76) | 4271 (26 RCTs) | ⊕⊝⊝⊝ VERY LOW 1, 3, 5 | |
| Adverse events ‐ Miscarriage | 68 per 1,000 | 55 per 1,000 (41 to 73) | OR 0.79 (0.58 to 1.08) | 2834 (18 RCTs) | ⊕⊝⊝⊝ VERY LOW 1, 2 | |
| Adverse events ‐ Multiple pregnancy | 80 per 1,000 | 80 per 1,000 (60 to 107) | OR 1.00 (0.73 to 1.38) | 2163 (8 RCTs) | ⊕⊝⊝⊝ VERY LOW 1, 2 | |
| Adverse events ‐ Gastrointestinal disturbances | 24 per 1,000 | 37 per 1,000 (12 to 112) | OR 1.55 (0.47 to 5.10) | 343 (3 RCTs) | ⊕⊝⊝⊝ VERY LOW 1, 4, 5 | |
| *The risk in the intervention group (and its 95% confidence interval) is based on the mean risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; OR: Odds ratio | ||||||
| GRADE Working Group grades of evidence High quality: We are very confident that the true effect lies close to that of the estimate of the effect Moderate quality: We are moderately confident in the effect estimate: The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different Low quality: Our confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect Very low quality: We have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of effect | ||||||
1Downgraded two levels due to very serious risk of bias; at high risk of bias in two domains.
2Downgraded one level due to serious imprecision; the event rate is low (< 300).
3Downgraded two levels due to very serious inconsistency (I2 = 81%) with differing directions of effect.
4Downgraded two levels due to very serious imprecision; the event rate is very low (n = 11).
5In practice, full downgrading not possible as evidence already graded as very low quality.