Summary of findings 1. Fresh compared to frozen embryo transfer (cumulatively) in assisted reproduction.
| Fresh compared to frozen embryo transfer (cumulatively) in assisted reproduction | ||||||
| Patient or population: women undergoing assisted reproduction Setting: assisted reproduction clinic Intervention: frozen embryo transfers only Comparison: fresh and frozen embryo transfers (conventional IVF) | ||||||
| Outcomes | Anticipated absolute effects* (95% CI) | Relative effect (95% CI) | № of participants (studies) | Quality of the evidence (GRADE) | Comments | |
| Risk with fresh and frozen embryo transfers | Risk with frozen embryo transfer only | |||||
| Live birth rate: cumulatively | 579 per 1000 | 589 per 1000 (567 to 627) | OR 1.08 (0.95 to 1.22) | 4712 (8 RCTs) | ⊕⊕⊕⊝ Moderatea | |
| OHSS: per cycle with ovarian hyperstimulation | 33 per 1000 | 9 per 1000 (6 to 13) | OR 0.26 (0.17 to 0.39) | 4478 (6 RCTs) | ⊕⊕⊝⊝ Lowa,b | |
| Ongoing pregnancy rate: cumulatively | 508 per 1000 | 495 per 1000 (436 to 551) | OR 0.95 (0.75 to 1.19) | 1245 (4 RCTs) | ⊕⊕⊕⊝ Moderatea | |
| Miscarriage rate: cumulatively | 118 per 1000 | 124 per 1000 (88 to 171) | OR 1.06 (0.72 to 1.55) | 986 (2 RCTs) | ⊕⊝⊝⊝ Very lowa,b,c | |
| Multiple pregnancy rate: cumulatively | 156 per 1000 | 140 per 1000 (101 to 188) | OR 0.88 (0.61 to 1.25) | 986 (2 RCTs) | ⊕⊝⊝⊝ Very lowa,b,c | |
| Time to pregnancy | Outcome could not be analysed. By design, time to pregnancy is shorter in the conventional strategy compared to the 'freeze all' strategy when the cumulative live birth rate is comparable, as embryo transfer is delayed in a 'freeze all' strategy. |
|||||
| *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; IVF: in vitro fertilisation; OHSS: ovarian hyperstimulation syndrome; OR: odds ratio; RCT: randomised controlled trial; RR: risk ratio | ||||||
|
GRADE Working Group grades of evidence High quality: further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: we are very uncertain about the estimate. | ||||||
aDowngraded one level due to serious risk of bias associated with lack of power calculation (unclear what determined end of study) and/or use of interim analysis that was calculated per transfer (unit of analysis error) with absence of adequate stopping rules (possible overestimation of treatment effect). bDowngraded one level due to serious imprecision: event rate less than 300. cDowngraded one level due to serious unexplained heterogeneity.