Failed embryo transfer doesn’t always mean there’s one missing answer. Dr Elias Tsakos, Medical Director of Embryoclinic, explains why implantation failure often comes down to several overlooked factors—from embryo genetics and sperm DNA to the uterus, timing, and even the transfer itself.
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When embryo transfer fails, the next step should not be guesswork but a careful, individualised review of embryo quality, the uterus, timing, technique, and overlooked health factors, according to Dr Elias Tsakos, MD, FRCOG – Medical Director, IVF specialist, Embryoclinic.
For many patients, the most frustrating part of failed implantation is being told there must be a single explanation. The picture is usually more complicated. Embryo quality depends on both egg and sperm, and both are equally important, which means a meaningful workup has to look at the couple rather than focusing on only one side.
That evaluation should begin before IVF whenever possible. On the female side, assessment of egg quality and quantity may include AMH, antral follicle count, hormonal testing, and karyotype. On the male side, a standard semen analysis may not be enough; further testing can include DNA fragmentation index, along with genetic testing such as karyotype and a cystic fibrosis test. If sperm DNA fragmentation is abnormal, it may be modifiable with vitamins and lifestyle changes, and that information can affect treatment planning.
The larger point is that testing should be individualised rather than arranged in a rigid tier system. Age, lifestyle factors that may adversely affect sperm, family history, and previous treatment history all matter. Dr Elias Tsakos said a proper fertility consultation can take 1.5 to 2 hours, because a complete picture requires careful history taking, review of prior data, and discussion with the couple about which tests are actually relevant.
Patients often put enormous weight on embryo grading, but appearance alone does not settle the question of whether an embryo can implant. morphology does not always predict genetic normality. A beautiful-looking embryo may still be abnormal, while a more modest-looking embryo may be the one that leads to pregnancy.
That is one reason embryo selection can involve more than a quick visual check. Embryos may be cultured to day 5 or day 6 and assessed further with time-lapse imaging before transfer decisions are made. At the same time, embryos that are not at least morphologically normal would not be transferred.
This is also where PGT-A enters the conversation, but with important limits. It is not a panacea, and it does not guarantee normality. Even a euploid embryo does not have a 100% chance of implantation. Rather than using PGT-A in all cycles, its value appears greater in selected situations: women older than 35, older men, cases of multiple implantation failures regardless of age, situations with three or more good-quality embryos in otherwise ideal conditions, or when a genetic anomaly has already been diagnosed. In someone under the age of 35 with no implantation failures and no recent relevant concerns, it would generally be avoided for the first or second transfers.
After several failed transfers of good-quality embryos, the focus should move strongly toward the uterine environment. Patients are often told that the endometrium looks fine because the thickness is acceptable, but the endometrium is more than the width on a scan. Modern ultrasound can assess it in the outpatient setting with minimal invasion through a vaginal scan, yet that still may not reveal the whole story.
The surrounding pelvic environment matters too. Hydrosalpinx should be excluded, and tubal assessment is important. Endometriosis may be present in up to 50% of infertility patients, with an even higher likelihood in those with implantation failure. Some conditions may not be detected by simple ultrasound, which is why diagnostic laparoscopy can still be the gold standard when implantation repeatedly fails.
The threshold for deeper uterine investigation may come earlier than many patients expect. After 2 failed implantations of good-quality embryos, further assessment may include hysteroscopy performed with expert hands and expert technology. Tissue obtained during hysteroscopy can be sent for histology and histopathology, including biopsy for endometritis. microbiome assessment and dysbiosis may also be relevant, especially when standard explanations have run out.
Repeated miscarriage and repeated implantation failure can leave behind damage that is easy to underestimate. The uterus and endometrium are extremely sensitive, and miscarriage itself can produce endometrial scarring. In patients with many miscarriages and failed implantations, the chance of an endometrial factor becomes very high.
One of the clearest examples is Asherman syndrome, in which adhesions or scar tissue cause the uterine cavity to collapse. It can be mild, moderate, or severe, and management may involve repeat hysteroscopies, precision excision of scar tissue, an IUD, antibiotics, probiotics, and PRP. Even then, the goal is not perfection. Asherman syndrome is chronic and, in this view, can never be treated 100%; the aim is to restore a reasonable endometrial cavity for embryo transfer.
In severe cases, damage may progress to absolute uterine factor infertility. That possibility becomes especially important when patients have had many losses, repeated failed transfers, and no obvious explanation for the embryo. It is also a reminder not to become so focused on immune protocols or hormone regimens that basic contributors such as progesterone absorption, iron status, and uterine scarring are missed.
Patients facing repeated failure often encounter a long list of add-on treatments. Some may have a place, but not as substitutes for a full evaluation. PRP is one example. After being sceptical for over a decade, Dr Elias Tsakos now believes it may have a role, possibly more for the endometrium than for the ovaries, in selected cases. It may be given by flushing or by injection through the hysteroscope, and timing is not standardised: after surgery, once or twice before embryo transfer, or 5 to 7 days before embryo transfer in a borderline endometrium. Quality control and preparation, however, remain major unanswered questions.
By contrast, endometrial scratch was more popular in the past, but the current evidence is not strong. Immunology may also play a role in implantation failure, but probably only a small one. Evaluation can include autoimmune conditions, natural killer cells, cytokines, and HLA factors, but only after essential factors have been assessed: embryo quality, embryo DNA, endometrial quality, surrounding pelvic factors, and hormonal balance.
If immune treatment is used, the starting point would be basic measures such as blood thinners. Low molecular weight heparin and steroids may be used if an immune response is diagnosed, and antiphospholipid syndrome is the condition with the clearest evidence for treatment. Intralipids may also be considered, but inflammation or infection should be assessed because they can affect the immune response.
Patients often assume that once a good embryo exists, the hard part is over. In reality, embryo transfer itself can be technically difficult, and the procedure matters enormously. The embryo should not remain out of the incubator for longer than 1.5 minutes, or 90 seconds, during transfer. If it is out longer than that, it should be returned to the incubator. Leaving embryos in the air for 30 to 45 minutes is harmful.
Difficult anatomy can complicate the process. A curved or retroverted uterus, or an angle at the level of the internal cervix, may require hysteroscopy, dilatation, or a mock transfer before the real attempt. Dilatation should be done four to six weeks before embryo transfer and should not be overenthusiastic; the cervix may be dilated up to seven or eight Hegar because it can stretch back. On the day of transfer, embryos should not be removed from the incubator unless the transfer can actually be completed successfully.
Even repeated cervical manipulation has consequences. It can increase inflammatory substances such as prostaglandins, which may affect implantation. That is why, in repeated implantation failure, the most experienced people should handle the embryo and perform the transfer.
For frozen embryo transfer, the preferred approach is often a natural cycle if the patient has normal menstrual cycles. In a woman under the age of 45 with normal cycles, a natural cycle would usually be favoured because there is less chance of getting it wrong than with a medicated cycle. Either way, frozen transfer cycles require very careful monitoring, especially of the luteal window.
Some patients also need a broader medical review. High DNA fragmentation may affect implantation, and ICSI does not overcome it. It may be optimised before IVF with antioxidants, vitamins, and similar measures, and it can influence whether sperm sorting methods are used. Ferritin is another often-overlooked marker. Iron affects folliculogenesis and the final stages of egg maturation, and ferritin matters in both assisted and non-assisted conception. If ferritin is below 30 before pregnancy, the risk of pregnancy loss is much higher; supplementation should be started, and if that does not work, an iron infusion should be discussed before proceeding.
When embryos do not implant, the most useful question is not “What is the one cause?” but “What has not yet been properly assessed?” The answer may lie in embryo genetics, sperm integrity, the endometrium, pelvic disease, transfer technique, timing, or a combination of several factors. The hopeful message is that failed implantation should trigger a more thoughtful investigation, not a narrower one.
Testing should be individualised. The right approach depends on age, lifestyle factors that may be adversely affecting sperm, family history, and a careful review of the full fertility history and prior data. There is no rigid tier system that suits everyone. The timing of more advanced testing should be discussed in pairs, because the relevance of each test varies by case.
Embryo morphology does not always reflect genetic normality. A beautiful-looking embryo may be genetically abnormal, while a modest-looking embryo may still lead to pregnancy. An embryo should be at least morphologically normal before transfer is considered. Embryos may be cultured to day 5 or day 6 and assessed with time-lapse before a decision is made. The concern is not only the failed implantation. Miscarriage, ectopic pregnancy, late miscarriage, or an ongoing pregnancy with an abnormal fetus are also possible outcomes.
PGT-A is most useful in women older than 35, men older than 45, cases of multiple implantation failures regardless of age, situations with three good-quality embryos in otherwise perfect conditions, or when a genetic anomaly has already been diagnosed. It is not appropriate for all cycles and should not be used routinely in unselected cycles. In transfer planning, normal embryos are prioritised first, then low-level mosaic embryos, and then other categories. Even a euploid embryo does not have a 100% chance of implantation.
The uterine and endometrial environment should be examined very carefully. Miscarriage itself can produce endometrial scarring, and many miscarriages place a heavy burden on the endometrium. If the endometrium has been severely damaged, an absolute uterine factor may be present. In confirmed absolute uterine factor infertility, the options are surrogacy or uterus transplantation.
PRP may have a place, possibly more for the endometrium than for the ovaries, and it can help in selected cases. It may be given by flushing or by injection through the hysteroscope. Timing is not standardised: it may be used after surgery, once or twice before embryo transfer, or 5 to 7 days before transfer when the endometrium is borderline. Quality control and preparation are still unresolved issues.
Endometrial scratch was more popular previously, but the evidence is not strong now. Hysteroscopy may be particularly useful in implantation failure, especially in women of advanced reproductive age.
Go back to basics: embryo quality, uterine factors, and surrounding factors. Confirm normal morphology and, if available, normal PGT-A results. Exclude hydrosalpinx, endometritis, and other pelvic pathology, including rare infections. The day of embryo transfer also matters, including which embryologist prepares the embryo, how the embryo is handled, and which clinician performs the transfer. In repeated implantation failure, the most experienced people should handle the embryos and perform the transfer.
Laparoscopy should be done to exclude pelvic infection, hydrosalpinx, and endometriosis. Another IVF cycle with PGT-A can then be considered. If menstrual cycles are normal, a frozen embryo transfer on a natural cycle is preferred. Careful monitoring of the transfer cycle is important because mistakes can happen in a medicated cycle.
There is no clear evidence for or against it. Using common sense, avoid anything too vigorous, but a normal sexual connection does not necessarily make a huge difference. There is no need to avoid it altogether, but extremes of physical exertion should be avoided.
Immunology appears to play a small role and should be evaluated only after the essential factors have been addressed. Possible assessments include autoimmune conditions, natural killer cells, cytokines, HLA factors, and immune signalling imbalance. Treatment options include blood thinners, low molecular weight heparin, steroids, and intralipids. Antiphospholipid syndrome is the condition with the strongest evidence. Inflammation or infection may also affect the immune response and should be assessed.
The transfer procedure is very important. An embryo should not be outside the incubator for longer than 1.5 minutes, or 90 seconds. If it is out longer than that, it should be returned to the incubator. Leaving embryos out in the air for 30 to 45 minutes is harmful. Excessive manipulation of the cervix can increase inflammatory substances such as prostaglandins, which may affect implantation.
If the uterus is curved or retroverted with an angle at the level of the internal cervix, hysteroscopy and dilatation should be considered. Dilatation should definitely be done before embryo transfer is attempted, ideally four to six weeks before transfer. It should not be overdone, but the cervix can be dilated up to 7 or 9 Hegar because it may stretch back. Embryos should not be taken out of the incubator unless the transfer can be completed successfully on that day.
Several factors may be involved. Egg and embryo quality related to PCOS may be one factor, but the tubes should be re-evaluated with a more reliable assessment, and laparoscopy should be considered. Ovarian drilling may help improve cycles and metabolic syndrome. Assessment should also include adhesions, endometriosis, and metabolic abnormalities, including insulin resistance, HbA1c, fasting insulin, fasting cortisol, and glucose. Continuous glucose monitoring could also be helpful.
Yes. High DNA fragmentation may affect implantation. ICSI does not overcome DNA fragmentation, but it can often be optimised before IVF with antioxidants, vitamins, and similar measures. It may also influence whether ICSI is combined with sperm sorting methods to identify the most suitable sperm.
Ferritin is also very important. Iron affects folliculogenesis and egg maturation, and ferritin matters in both assisted and non-assisted conception. If ferritin is less than 30 before pregnancy, the risk of pregnancy loss is much higher. Low ferritin may require supplementation, and if that does not work, an iron infusion should be discussed before proceeding.
Age-related embryo quality is the main limiting factor, although other factors can also exist. The recommended strategy is to pursue IVF, generate as many eggs as possible with the right drug dose, create blastocysts, freeze them, and build a bank of at least two to three good-quality embryos over three to four months. PGTA testing should be done. If one normal embryo is obtained, the implantation chance is similar to that of a 40-year-old. If no deployed embryos are available, donor eggs may be the only forward path.
