In a 2026 meta-analysis, researchers combined the results of 17 studies and found that day 7 blastocysts had lower live birth rates than day 5 or day 6 blastocysts, even when only euploid embryos were compared.
Day 5 vs Day 6 vs Day 7
In a 2025 meta-analysis, day 5 blastocysts were linked to higher pregnancy and live birth rates than day 6 blastocysts, while newborn outcomes were similar and poor quality day 5 embryos showed comparable potential to good quality day 6 embryos.
A 2025 study found that while poor quality blastocysts are less likely to be euploid, some can still lead to healthy live births. Tested poor quality embryos had higher live birth rates and lower miscarriage rates than untested ones, especially when they developed by day 5 instead of day 6.
A new study showed that day 7 embryos may develop more slowly because of stress and disrupted signaling in the inner cell mass, which might help explain their lower success rates.
The ASRM has released their 2024 committee opinion on the use of PGT-A, covering the use of PGT-A for patients with a good prognosis, advanced age, donor eggs, recurrent pregnancy loss and more.
Researchers in a 2023 study found that day 7 euploids have the lowest ongoing pregnancy rate, when compared to day 5 and 6 euploids. These embryos were mostly poor quality.
Researchers in a 2023 study show that poor quality embryos have acceptable live birth rates compared to good and fair quality embryos, with only a slight increase in pregnancy loss and no differences in perinatal outcomes.
Researchers in a 2023 study found that arrested embryos have a high degree of aneuploidy, which is mainly due to mitotic errors that occur after fertilization. In a separate analysis of non-arrested embryos, they found that good quality/day 5 embryos have less aneuploidies compared to poor quality/day 6 and 7 embryos.
Researchers in a 2023 study found that embryos that take longer to develop had lower quality scores for both the ICM and trophectoderm, and had reduced clinical pregnancy and live birth rates.
Researchers in a 2023 study combined the results of 74 studies to investigate what factors contribute to euploid live birth and miscarriage rates, identifying embryo quality, maternal age, specific diagnoses, repeat freeze/thaw, and other factors.
Researchers in a 2023 study evaluated factors affecting pregnancy outcomes after euploid transfer, and found that double euploid transfer, BMI, type of FET protocol, and the day of embryo biopsy all had an impact.
Researchers in a 2023 study found comparable pregnancy and neonatal outcomes when transferring a day 5 poor quality or a day 6 good quality embryo.
Researchers in a 2022 study showed that extending embryo culture to day 7 increases the number of useable blastocysts, particularly for older women.
Researchers in a 2019 study compared euploid transfer outcomes for day 5, 6 or 7 euploids, finding that day 7 embryos have good potential.
Not sure what your embryo grade means—or if it affects your chances of success? This guide walks you through everything from day 3 and day 5 grading systems to what each number and letter combo (like 3BB or 5AA) actually means. You’ll also find success rate research, embryo photos, and insights from a former embryologist to help make sense of your report.