Why Do PGT-A Normal Embryos Fail to Implant? | Ivy Surrogacy

🔑 Key Takeaways

A PGT-A normal (euploid) embryo does not guarantee pregnancy. The live birth rate per transfer of a single euploid frozen blastocyst is generally between 50% and 60%, meaning roughly 1 in 3 will not result in a live birth.
Scientists call this "the black box of implantation." A landmark 2023 review in Human Reproduction Update analyzed over 370 studies and concluded that the causes of euploid embryo failure remain only partially understood.
Three categories of factors drive implantation failure: embryonic issues beyond chromosomes (gene expression, mitochondrial function, undetected mosaicism), uterine and endometrial conditions (lining thickness, receptivity timing, chronic endometritis), and systemic health factors (thyroid, autoimmune conditions, BMI).
Embryo grade and development day still matter — even among euploid embryos. Day 5 blastocysts outperform Day 6 and Day 7, and higher-grade embryos (AA, AB) have better outcomes than lower-grade ones.
Surrogacy improves many uterine variables but does not eliminate embryonic factors. The embryo’s intrinsic biology travels with it, regardless of whose uterus receives it.
A failed transfer does not predict future failure. Cumulative success rises with each additional euploid transfer, and your fertility team can investigate and optimize conditions before the next attempt.

Everything looked perfect on paper.

A top-grade blastocyst. PGT-A confirmed euploid — all 46 chromosomes present and accounted for. The surrogate’s lining was thick, her protocol on track. The transfer went smoothly.

And then, ten days later — a negative beta.

At Ivy Surrogacy, we see this scenario more often than anyone would like. Intended parents who have invested months of preparation, tens of thousands of dollars, and an immeasurable amount of hope are left asking one devastating question:

How can a genetically normal, high-grade embryo still fail to implant?

It’s a question that even reproductive medicine hasn’t fully answered yet. Scientists call it “the black box of implantation” — a term used in a landmark 2023 systematic review published in Human Reproduction Update that analyzed over 370 studies on this exact puzzle.

But while the mystery isn’t completely solved, we now know far more than we did even five years ago. In this post, we’ll walk you through the current scientific understanding — clearly and honestly — so you can navigate your journey with realistic expectations and informed confidence.

First, Let’s Set Realistic Expectations: What Are the Actual Numbers?

One of the most common misconceptions is that a PGT-A normal embryo should guarantee pregnancy. It doesn’t — and understanding the real numbers is the first step toward managing expectations.

According to aggregated clinical data cited in peer-reviewed literature, the live birth rate per transfer of a single euploid (PGT-A normal) frozen blastocyst is generally between 50% and 60%. Some individual studies report rates as high as 65–70% for Day 5, top-grade embryos in younger patients, while others report rates closer to 40–50% depending on patient characteristics.

A 2022 comprehensive review published in Fertility and Sterility Reviews confirmed that even with the most favorable conditions, roughly 1 in 3 euploid embryos will not result in a live birth. Euploid embryos have been shown to have implantation failure rates of 18–27%, and in some study definitions, as high as 33%.

That’s not a failure of the embryo alone — it’s a reflection of how extraordinarily complex human implantation truly is.

👉 Try it yourself: Use our Embryo Transfer Success Rate Calculator to estimate your per-transfer and cumulative live birth probability based on age, blastocyst day, and morphology.

So, What’s Inside “the Black Box”? The Science Behind Implantation Failure

Researchers generally organize the causes of euploid implantation failure into three categories: embryonic factors, uterine and endometrial factors, and systemic (whole-body) factors. Let’s explore each.

Diagram of euploid blastocyst approaching the endometrial surface during the implantation window, illustrating three categories of implantation failure: embryonic factors (gene expression, mitochondria, mosaicism), uterine factors (receptivity, thickness, inflammation), and systemic factors (thyroid, autoimmune, BMI, vitamin D)

1. Embryonic Factors: When “Normal Chromosomes” Isn’t the Whole Story

PGT-A is a powerful tool — but it has defined boundaries. It confirms that an embryo has the correct number of chromosomes (46). What it cannot evaluate is far broader:

Gene expression and epigenetics. An embryo carries approximately 25,000 genes that must activate and deactivate in a precisely coordinated sequence — like an orchestra performing a complex symphony. If the timing of this gene expression is off at a critical moment, the embryo may fail to implant or stop developing, even though every chromosome is accounted for. Current technology cannot test for this in clinical settings.

Mitochondrial function and energy metabolism. Embryo development is energy-intensive. Mitochondria — the cellular powerhouses — must function properly for the embryo to hatch, attach, and invade the uterine lining. Subtle mitochondrial deficiencies can compromise implantation, but these are not detectable by PGT-A.

Mosaicism that escapes detection. PGT-A biopsies 5–10 cells from the trophectoderm (the outer layer that becomes the placenta). It’s possible that the biopsied cells are euploid while other parts of the embryo carry abnormal cells. This is known as undetected mosaicism, and it represents a known limitation of any biopsy-based test.

Embryo morphology still matters. Even among euploid embryos, higher-grade blastocysts (such as AA or AB) consistently show better implantation and live birth rates than lower-grade ones (BB, BC, CC). Research on outcomes by morphology found that Day 5 good-quality euploid blastocysts had sustained implantation rates around 86%, compared to roughly 51% for Day 6 blastocysts — even though both were chromosomally normal.

Day of development matters too. Embryos that reach the blastocyst stage on Day 5 generally outperform those that develop on Day 6, and Day 7 blastocysts show substantially reduced success rates — approximately 30% lower than Day 5. This may reflect underlying differences in embryo vitality that go beyond chromosome count.

Sperm DNA fragmentation — the often-overlooked paternal factor. When an embryo fails to implant, the conversation tends to focus on egg quality or the uterine environment. But the sperm contributes half of the embryo's DNA, and high levels of sperm DNA fragmentation can compromise embryonic development even when the resulting blastocyst appears normal and tests euploid. Damaged paternal DNA may lead to errors in gene activation after fertilization — errors that PGT-A cannot detect. For intended parents experiencing unexplained recurrent failure, a sperm DNA fragmentation test is a reasonable part of the diagnostic workup.

2. Uterine and Endometrial Factors: When the “Soil” Isn’t Ready

Think of the uterus as a garden and the endometrium (uterine lining) as the soil. Even the healthiest seed won’t grow if the soil conditions aren’t right.

Endometrial thickness. Research involving over 20,000 frozen embryo transfer cycles has demonstrated that pregnancy rates decrease significantly when endometrial thickness falls below 7 mm. While pregnancies can occur with thinner linings, they are less likely and may carry higher complication risks.

👉 Learn more: Uterine Lining in Embryo Transfer: A Guide for Surrogates and Intended Parents

The Window of Implantation (WOI). For an embryo to implant, it must arrive at the endometrium during a narrow receptive window — typically lasting 24 to 48 hours. If the timing between embryo transfer and the endometrium’s readiness is misaligned, even a perfect embryo won’t attach. A pivotal study published in Fertility and Sterility found that endometrial compaction (a slight decrease in thickness during progesterone exposure) was strongly associated with implantation success — patients whose lining compacted had an 83% clinical pregnancy rate, compared to just 19% in those whose lining thickened during the progesterone phase. Notably, the morphological grade of the euploid embryos had no correlation with pregnancy outcomes in this study — endometrial receptivity was the dominant factor.

👉 Dive deeper: ERA Test in IVF & Surrogacy: What Parents Should Know

Chronic endometritis (CE). This is a low-grade, often silent infection or inflammation in the uterine lining caused by bacterial infiltration. It is far more common than most people realize: studies suggest CE is present in approximately 30–57% of women with recurrent implantation failure. It can usually be diagnosed via endometrial biopsy and treated with a course of antibiotics.

Silent endometriosis. In some cases, endometriosis may be present without obvious symptoms but still create an inflammatory uterine environment that hinders implantation. Emerging research has explored biomarkers such as BCL6 (tested via endometrial biopsy) as a way to identify silent endometriosis in patients with unexplained RIF. While this testing is not yet part of standard guidelines, it represents a growing area of clinical interest.

Structural abnormalities. Uterine fibroids (especially submucosal ones), polyps, scar tissue from prior surgeries, and a uterine septum can all physically interfere with embryo attachment. Hydrosalpinges — fluid-filled fallopian tubes — are another recognized factor; the fluid can leak into the uterus and create a hostile environment for implantation.

Adenomyosis. This condition — where endometrial tissue grows into the muscular wall of the uterus — is increasingly recognized as a significant contributor to recurrent implantation failure. Adenomyosis creates a chronic inflammatory environment, disrupts uterine contractility, and may impair blood flow to the endometrium. It is also one of the more common medical reasons intended parents pursue surrogacy, as the condition can be difficult to treat and may persist despite intervention.

Prior cesarean section. Emerging data suggests that a history of C-section may lower implantation rates for euploid embryos, potentially due to scar tissue at the transfer site or altered blood flow to the endometrium.

3. Systemic Factors: What’s Happening in the Whole Body

Implantation doesn’t happen in isolation. The surrogate’s or mother’s overall health plays a significant supporting role.

Thyroid dysfunction. Uncontrolled hypothyroidism or Hashimoto’s thyroiditis can interfere with pregnancy establishment. Most IVF protocols screen for thyroid function, but subtle subclinical issues can still slip through.

Thrombophilia and autoimmune conditions. Antiphospholipid syndrome and certain blood clotting disorders have been associated with implantation failure and early pregnancy loss. The American Society for Reproductive Medicine (ASRM) recommends thrombophilia screening for patients with recurrent implantation failure.

Vitamin D deficiency. The active form of vitamin D is secreted by the endometrium and influences genes essential for implantation. While evidence is still mixed, many clinics include vitamin D assessment as part of a comprehensive workup.

BMI and metabolic health. Elevated BMI has been associated with lower implantation rates and higher miscarriage risk, likely due to increased inflammation, hormonal imbalances, and altered insulin sensitivity. However, within moderate ranges, BMI alone may not be a decisive factor — and at Ivy Surrogacy, all surrogates undergo thorough medical screening, including BMI assessment, before being cleared for transfer.

Lifestyle factors. Cigarette smoking affects both egg quality and blood flow to the uterus. Chronic stress, poor sleep, and nutrient deficiencies may also play contributing roles, though the evidence for these is less definitive.

Does the Embryo Transfer Procedure Affect Implantation Rates?

Factors during the embryo transfer procedure can also influence outcomes:

Difficult transfers. If the catheter encounters resistance, requires multiple attempts, or causes cervical trauma, implantation rates may be reduced — even with euploid embryos.

Freeze-thaw cycles. While modern vitrification techniques achieve embryo survival rates above 98%, embryos that have been biopsied and frozen twice (for example, after re-biopsy) may have slightly lower implantation potential.

Laboratory conditions. Culture media composition, incubator conditions, and the skill of the embryologist all influence embryo development in ways that PGT-A cannot capture. Two embryos with identical grades from two different labs may not have the same implantation potential.

A Special Note for Surrogacy Journeys

In gestational surrogacy, many of the uterine factors are actually more favorable — surrogates are typically younger, have proven fertility with prior successful pregnancies, and undergo thorough medical screening. This is one of the reasons surrogacy success rates tend to be higher than self-transfer for many intended parents.

However, surrogacy does not eliminate all variables. The embryo’s intrinsic biology — its gene expression, mitochondrial health, and development dynamics — travels with the embryo regardless of whose uterus receives it. A euploid embryo that carries hidden embryonic limitations will face the same challenges in a surrogate as it would in any other setting.

This is why, at Ivy Surrogacy, we always counsel intended parents that each embryo transfer — even with a perfect-looking embryo — carries inherent uncertainty. It’s not a reflection of anyone’s failure. It’s the biological reality of human reproduction.

👉 Also read: Blighted Ovum After PGT-A Embryo Transfer: Causes, What to Expect, and How to Move Forward

What Can Be Done After a Failed Euploid Transfer?

A failed transfer is heartbreaking — but it’s not the end of the road. Your fertility doctor will work with you to investigate possible causes and optimize conditions before the next attempt.

Common next steps may include a detailed review of the uterine environment (such as a hysteroscopy or additional imaging), assessment of endometrial receptivity and hormonal balance, screening for underlying conditions like chronic endometritis or thrombophilia, and evaluation of lifestyle or systemic factors that may be modifiable.

Every case is different, and the right workup depends on your individual history and circumstances. The most important thing is to have an open, thorough conversation with your reproductive endocrinologist about what was learned from the failed cycle and what adjustments might improve outcomes next time.

At Ivy Surrogacy, our team — many of whom come from clinical backgrounds — is here to help you navigate these conversations, coordinate with your IVF clinic, and ensure no stone is left unturned.

The Bottom Line: Hope, Grounded in Science

If you’ve experienced a failed transfer with a PGT-A normal embryo, please know this: you are not alone, and it is not your fault — or your surrogate’s fault — or your doctor’s fault.

Human reproduction, even with the most advanced technology available, remains one of nature’s most complex and imperfectly understood processes. A 2024 study in Reproductive Biology and Endocrinology found that approximately 20% of patients failed to achieve sustained implantation after transferring up to three euploid blastocysts — confirming that factors beyond chromosomal status play a meaningful role in outcomes.

But here’s the encouraging part: the cumulative probability of success rises with each transfer. For patients with multiple euploid embryos available, the odds of eventually achieving a live birth are significantly higher than any single-transfer number suggests. A failed first transfer does not predict failure on the second or third.

At Ivy Surrogacy, we walk with our intended parents through every outcome — the joyful ones and the heartbreaking ones. We believe that understanding the science helps reduce fear and empowers better decision-making. And we’re here to ensure that every step of your journey is supported with honesty, expertise, and compassion.

Frequently Asked Questions (FAQ)

Q: If my embryo passed PGT-A, why didn’t it implant?

PGT-A confirms that an embryo has the correct number of chromosomes, but it doesn’t evaluate everything that matters for implantation. Gene expression timing, mitochondrial energy, undetected mosaicism, and endometrial receptivity all play critical roles that fall outside the scope of chromosomal screening. Having normal chromosomes is necessary — but not sufficient — for a successful pregnancy.

Q: What is the actual success rate of transferring a PGT-A normal embryo?

The live birth rate per single euploid frozen embryo transfer is generally between 50–60%, depending on factors like the egg provider’s age, the day of blastocyst development (Day 5 vs. Day 6 vs. Day 7), and embryo morphology grade. You can estimate your personal probability using our Embryo Transfer Success Rate Calculator.

Q: Does using a surrogate increase the chance of a euploid embryo implanting?

In many cases, yes. Gestational surrogates are typically younger, have proven uterine receptivity through prior successful pregnancies, and undergo comprehensive medical screening. These factors can create a more favorable uterine environment. However, surrogacy cannot overcome embryonic factors like gene expression errors or mitochondrial dysfunction that travel with the embryo itself.

Q: Should I ask my doctor about an ERA test after a failed euploid transfer?

The ERA (Endometrial Receptivity Analysis) is designed to identify whether a woman’s window of implantation is shifted from the standard timing. While current guidelines from both ASRM and ESHRE do not recommend ERA for routine use, it may be considered for patients with multiple unexplained failed transfers. Discuss with your reproductive endocrinologist whether it’s appropriate for your situation. 👉 Learn more about the ERA test

Q: How many failed euploid transfers should I experience before additional testing is recommended?

There is no universal threshold, and the answer depends on your individual circumstances. Some clinics recommend additional investigation after two failed euploid transfers; others may suggest it sooner if there are other risk factors. The most important step is an open conversation with your fertility doctor about a personalized evaluation plan.

Q: Does embryo grade matter if the embryo already passed PGT-A?

Yes. Even among chromosomally normal embryos, morphology grade remains a significant predictor of implantation and live birth. Higher-quality blastocysts (AA, AB) consistently outperform lower-grade ones (BB, BC, CC), and Day 5 embryos generally outperform Day 6 and Day 7 embryos.

Q: Can a failed transfer happen because of the surrogate?

While uterine and systemic factors in the surrogate can contribute — such as an undiagnosed thin lining, a shifted implantation window, or an underlying condition — surrogates at reputable agencies like Ivy Surrogacy are screened extensively before transfer. In many cases of euploid transfer failure, the embryo’s own biology is the primary factor, not the carrier.

Q: Is it worth trying again after a failed euploid transfer?

In most cases, absolutely. A single failed transfer is well within the expected range of outcomes for even the highest-quality embryos. The cumulative live birth rate rises meaningfully with each additional euploid transfer. A 2024 study confirmed that success rates per transfer remain stable across attempts, and your doctor can use information from the failed cycle to optimize the next one.

Related Resources from Ivy Surrogacy

Have questions about your embryo transfer results or next steps? Contact Ivy Surrogacy for a personalized consultation.

References

Cimadomo, D., et al. (2023). “Opening the black box: why do euploid blastocysts fail to implant? A systematic review and meta-analysis.” Human Reproduction Update, 29(5), 570–633. Read the study →
Reshef, E.A., et al. (2022). “A review of factors influencing the implantation of euploid blastocysts after in vitro fertilization.” Fertility and Sterility Reviews, 3(2), 105–120. Read the study →
Casper, R.F. (2019). “Why do euploid embryos fail to implant?” Fertility and Sterility, 111(4), Supplement, e3. Read the study →
ASRM Practice Committee (2024). “The use of preimplantation genetic testing for aneuploidy: a committee opinion.” Read the opinion →
Almohammadi, A., et al. (2024). “The reproductive potential of vitrified-warmed euploid embryos declines following repeated uterine transfers.” Reproductive Biology and Endocrinology, 22, Article 23. Read the study →
Management strategies following implantation failure of euploid embryos. (2024). Reproductive Medicine and Biology. Read the study →
Awadalla, M., et al. (2021). “Effect of age and morphology on sustained implantation rate after euploid blastocyst transfer.” Reproductive BioMedicine Online, 43(4), 694–700. Read the study →
Pirtea, P., et al. (2021). “Defining Recurrent Implantation Failure: a profusion of confusion or simply an illusion?” Frontiers in Endocrinology. Read the study →

Why Do PGT-A Normal Embryos Fail to Implant? Euploid Success Rates & Causes