Day 7 Euploid Embryos: A 24.1% Live Birth Rate, Not a Lost Cause

Day 7 euploid embryos can lead to live birth after IVF, even when their development is slower than that of day 5 or day 6 blastocysts. In a study of 3,338 women undergoing single euploid frozen embryo transfer, the live birth rate was 24.1% for day 7 embryos, compared with 65.0% for day 5 and 55.0% for day 6. Lower odds, however, did not mean no chance of a baby.

The study also found no clear differences in the obstetric and neonatal outcomes examined among births from the three groups, including birthweight and gestational age. The findings offer evidence for a difficult question: should an embryo be dismissed simply because it took longer to develop?

In IVF, an embryo that becomes a blastocyst on the fifth day after fertilization is generally considered to have developed at a favorable pace. Day 6 blastocysts are also commonly frozen for later transfer. As embryos reach the late blastocyst stage, treatment planning moves toward freezing or transfer around the implantation stage rather than indefinite laboratory culture. But what about an embryo that does not reach the blastocyst stage until day 7?

The question can be particularly painful when this is the last embryo a patient has obtained. Is an embryo that developed so slowly worth keeping and transferring? The recent study provides concrete numbers: day 7 embryos classified as euploid could result in a baby, although pregnancy and live birth were substantially less likely than after day 5 or day 6 euploid embryo transfer.

What the study of 3,338 euploid embryo transfers compared

The research, published online in Reproductive BioMedicine Online in September 2026, analyzed outcomes in 3,338 women who received a single frozen-thawed blastocyst classified as euploid after preimplantation genetic testing.

The women were grouped by the day on which their embryo reached the blastocyst stage: 1,338 in the day 5 group, 1,585 in the day 6 group, and 415 in the day 7 group. The researchers compared pregnancy, live birth, obstetric and neonatal outcomes.

The comparison was not simply between embryos of different ages. All transfers involved a single embryo classified as euploid. Holding this important chromosome variable more consistent allowed the researchers to examine how the time required to become a blastocyst was associated with reproductive outcomes.

Live birth rates: 65.0% on day 5, 55.0% on day 6 and 24.1% on day 7

Positive pregnancy-test rates were 80.6% for day 5 embryos and 75.0% for day 6 embryos, compared with 40.0% for day 7 embryos. Clinical pregnancy rates, reflecting pregnancy confirmed clinically such as by ultrasound, were 72.3%, 64.4% and 30.6%, respectively.

For live birth, the corresponding rates were 65.0%, 55.0% and 24.1%. Of the 415 women who received a day 7 euploid embryo, 100 gave birth.

These were all embryos classified as euploid. A reassuring chromosome result may lead patients to assume that implantation potential is similar across embryos, but that was not what the study found. The longer an embryo took to become a blastocyst, the lower the observed pregnancy and live birth rates. Chromosome status alone therefore did not explain all of its developmental potential.

Does a lower success rate mean a day 7 embryo should be discarded?

The results should not be read as meaning that day 7 embryos have no value. For patients, 24.1% can be viewed from another perspective.

It is clearly lower than the 65.0% live birth rate for day 5 embryos. Yet approximately one in four women receiving a day 7 euploid embryo in this study did have a baby. That opportunity may be especially important when no day 5 or day 6 euploid embryos remain.

Advances in embryo culture have made it increasingly possible to observe and freeze embryos that reach the blastocyst stage on day 7. The study supports the distinction between lower transfer efficiency and absent reproductive potential.

Rather than judging an embryo solely by the fact that it developed on day 7, decisions need to consider its chromosome result and morphology alongside the patient's age, treatment history and other available embryos.

Fewer births, but comparable measured outcomes among babies born

Another important finding concerned what happened when a transfer did result in a birth. Day 7 embryos were less likely to lead to pregnancy and live birth, but the main obstetric and neonatal outcomes examined did not show clear differences from those following day 5 or day 6 transfers.

The researchers did not find clear evidence of worse measured outcomes for day 7 births, including birthweight, gestational age and the obstetric and neonatal complications assessed.

In everyday terms, the hurdle of reaching pregnancy and birth was higher, but the outcomes after a successful birth were not clearly worse in the measures studied. This is not proof that every safety outcome is equivalent. There were fewer day 7 transfers than day 5 or day 6 transfers, and larger follow-up studies are needed to assess safety more firmly.

Euploid embryos do not all have the same reproductive potential

A euploid PGT result is valuable information. It does not mean that every embryo receiving that result has the same chance of implantation or live birth.

In this study, the live birth rates differed substantially according to the day of blastocyst development, despite all embryos being classified as euploid. Developmental speed, morphology and other biological characteristics may contribute to reproductive potential alongside chromosome status.

For patients with day 5, day 6 and day 7 euploid embryos available, these results support the existing clinical reasoning behind prioritizing faster-developing embryos. For someone with only a day 7 euploid embryo remaining, the situation is different.

Its success rate was lower, but approximately one in four day 7 transfers in this cohort led to a baby. An embryo that developed late and an embryo that cannot result in birth are not the same thing. That distinction matters when evaluating a hard-won final embryo.

Study source and limits

This article is based on “Day 7 euploid blastocyst transfer: lower efficacy, but comparable reproductive outcomes to Days 5-6,” published online in Reproductive BioMedicine Online in September 2026, article 105971. The investigators included researchers from the First Affiliated Hospital of Zhengzhou University and the First Affiliated Hospital, Sun Yat-sen University, China. DOI: 10.1016/j.rbmo.2026.105971.

The study compared 3,338 women receiving single euploid frozen embryo transfers. Its group-level results do not predict an individual patient's outcome, and the smaller day 7 group limits how confidently uncommon neonatal or obstetric risks can be assessed.