Clinical outcomes of Day-7 blastocysts: a systematic review and meta-analysis.
Julie Firmin, Bastien Ducreux, Haitam Saidessalam et al.
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In 30 seconds
This systematic review and random-effects meta-analysis compared frozen Day-7 blastocyst transfers with Day-5 and Day-6 transfers. It included 17 retrospective studies; across 2,908 Day-7 transfers, clinical pregnancy and live birth rates were significantly lower for Day-7 embryos. Compared with Day-5, the pooled odds ratio for live birth was 0.23 (95% CI 0.16-0.33); compared with Day-6, it was 0.37 (95% CI 0.28-0.49). Lower clinical pregnancy and live birth rates also persisted among PGT-A euploid embryos. Perinatal data were limited but described as overall reassuring.
Key findings
- Day-7 transfers had lower live birth odds than Day-5 transfers (OR 0.23, 95% CI 0.16-0.33) and Day-6 transfers (OR 0.37, 95% CI 0.28-0.49).
- Among PGT-A euploid embryos, live birth odds remained lower for Day-7 than Day-5 (OR 0.21, 95% CI 0.17-0.28) and Day-6 (OR 0.36, 95% CI 0.28-0.46).
- Miscarriage odds were higher for Day-7 than Day-5 transfers (OR 1.54, 95% CI 1.04-2.30), and higher in the euploid comparison (OR 2.78, 95% CI 1.57-4.89).
- Euploidy rates were significantly lower for Day-7 blastocysts than for Day-5 and Day-6 blastocysts.
Why it matters
The findings indicate that later blastocyst development is associated with lower transfer success, including when embryos are classified as euploid. This helps contextualise expected outcomes when Day-7 embryos are considered, while the review’s suggestion that they may contribute to cumulative live births—particularly for poor-prognosis patients—supports viewing their potential in the broader treatment course rather than from transfer outcomes alone.
What to keep in mind
All 17 included studies were retrospective, pooled analyses showed low to high heterogeneity, and perinatal outcome data were limited.