It is amazing to me that your clinic is so closed minded. Here is an article I wrote on implantation dysfunction. If you would like to have an online discussion with me, please email Patti at concierge@sherIVF.com and she will set it up.

Implantation Dysfunction: An Under-recognized Cause of Reproductive Failure

Sher Fertilty Solutions ( SFS)

For decades, one explanation has dominated the world of in vitro fertilization (IVF): if treatment fails, the embryo must have been abnormal.

It is a simple and convenient explanation. After all, embryo quality is unquestionably one of the most important determinants of reproductive success. Indeed, approximately 70–80% of IVF failures result from embryo incompetence, most commonly due to chromosomal abnormalities (aneuploidy) associated with advancing maternal age, diminished ovarian reserve (DOR), or, less commonly, significant sperm dysfunction. Today, sophisticated genetic testing (PGT-A) can identify many chromosomally normal embryos before transfer, and younger women with normal ovarian reserve are expected to produce a high proportion of embryos capable of developing into healthy pregnancies.

Yet many women continue to experience repeated IVF failure or recurrent pregnancy loss despite transferring embryos that should have had an excellent chance of implanting.

Why?

Because successful reproduction depends on far more than the quality of the seed. It also depends on the quality of the soil.

This “Seed and Soil” concept has guided much of our work. Even the healthiest seed cannot flourish in unreceptive soil.

Likewise, even a chromosomally normal embryo may fail if the uterus is not structurally, hormonally, or immunologically prepared to receive and nurture it.

This simple concept helps explain one of the most overlooked causes of reproductive failure……implantation dysfunction.

Although embryo quality remains the principal determinant of IVF success, I believe that approximately 20–30% of repeated IVF failures, unexplained infertility, and recurrent pregnancy losses result primarily from implantation dysfunction rather than embryo incompetence. Recognizing this distinction is critical because the diagnosis, investigation, and treatment are fundamentally different.

When a young woman with normal ovarian reserve repeatedly fails to conceive, or when chromosomally normal (euploid) embryos repeatedly fail to implant, the obvious question should no longer be, “What’s wrong with the embryo?” Rather, it should be, “Could the problem lie with implantation?”

Unfortunately, this question is often never asked.

Much of modern IVF has focused on improving embryo development, refining laboratory techniques, and selecting the best embryos for transfer. These advances have transformed reproductive medicine and have dramatically improved pregnancy rates. However, creating an excellent embryo represents only half of the journey. The embryo must still establish a complex biological dialogue with the uterus before implantation can occur.

Embryo implantation is not a passive event. It is one of the most sophisticated interactions in human biology. During a brief and highly regulated “window of implantation,” the embryo and the uterine lining exchange molecular signals that determine whether the embryo will be accepted, nourished, and allowed to develop into a healthy placenta, or whether implantation will fail before pregnancy has even begun.

This process depends upon three essential requirements:

• A structurally normal uterine cavity.
• A healthy, receptive endometrium of adequate thickness.
• A properly regulated immunologic

environment that recognizes the embryo as one to be accepted rather than rejected.

Failure of any one of these 3 components may prevent or impair implantation, regardless of embryo quality.

For practical purposes, implantation dysfunction can be divided into two broad categories:

1. ANATOMICAL IMPLANTATION DYSFUNCTION

Structural abnormalities of the uterus remain one of the commonest and fortunately one of the most treatable causes of implantation dysfunction. Even subtle abnormalities of the uterine cavity may interfere with embryo attachment by disrupting the normal architecture of the endometrium, impairing blood flow, or creating a localized inflammatory response that prevents normal implantation.

A. Irregularities of the Uterine Surface

Many uterine abnormalities are surprisingly small yet biologically significant. Submucosal fibroids, endometrial and placental polyps and intrauterine adhesions may all interfere with implantation by creating localized inflammation resembling the effect produced by an intrauterine contraceptive device (IUD). Even lesions measuring only a few millimeters can significantly reduce implantation potential when located beneath or protruding into the uterine cavity.

Uterine fibroids located entirely within the muscular wall of the uterus (intramural) usually do not impair fertility. However, fibroids that distort or encroach upon the uterine cavity ( sub-mucous) may compromise implantation by reducing blood flow, interfering with estrogen delivery to the endometrium, and preventing normal development of a receptive uterine lining.

Because IVF is physically, emotionally, and financially demanding, every effort should be made to identify correctable uterine defects before an embryo is transferred to the uterus. This is especially important in women with” unexplained”IVF failure or recurrent pregnancy loss (RPL).

Several diagnostic techniques are available. Hysterosalpingography (HSG) provides useful information regarding the shape of the uterine cavity but may miss smaller lesions. Saline infusion sonography (hysterosonography or HSN) has become one of the most valuable office-based investigations because it is minimally invasive, relatively inexpensive, and highly accurate when performed by experienced operators. By distending the uterine cavity with sterile saline during transvaginal ultrasound examination, even very small polyps, fibroids, adhesions, or uterine septa can often be detected with remarkable precision.

Hysteroscopy remains the definitive diagnostic and therapeutic procedure because it allows direct visualization of the uterine cavity while simultaneously permitting surgical correction of abnormalities.

Approximately one in eight women preparing for IVF harbors a uterine lesion that deserves correction before embryo transfer. Removing these abnormalities often restores a more receptive uterine environment and significantly improves the likelihood of successful implantation.

B. Thin Endometrium (The Receptive Uterine Lining)

A normal uterine cavity alone is not sufficient. The lining of the uterus must also become adequately developed under the influence of estrogen before it can support implantation.

More than three decades ago, we demonstrated that ultrasound measurement of endometrial thickness d configuration during the late proliferative phase (i.e., the time of maximal estrogen influence) could predict implantation potential. We found that an endometrial thickness exceeding approximately 9 mm with a trilateral configuration , at ovulation, egg retrieval, or immediately prior to the initiation of progesterone therapy was associated with optimal embryo implantation rates, whereas linings measuring less than 8 mm were associated with implantation failure or early pregnancy loss in the overwhelming majority of cases. Endometrial thickness between 8 and 9 mm represented an “intermediate” zone where pregnancies certainly occurred, but at somewhat reduced rates.

Why does this matter?

The endometrium consists of two distinct layers. A basal layer serves as the regenerative foundation from which the superficial functional layer ( which comprised about three quarters of the full endometrial layer) develops each menstrual cycle under estrogen stimulation. It is this functional layer that receives the implanting embryo and later forms the maternal component of the placenta. It is also this layer that sheds at the time of menstruation . If the basal layer has been damaged or has lost its ability to respond appropriately to estrogen, adequate endometrial development may never occur.

Several conditions can produce a persistently thin or poorly receptive endometrium. The commonest include chronic endometritis following miscarriage, abortion, or childbirth; excessive trauma from aggressive dilatation and curettage (D&C); prolonged and repeated ( >2) exposures to consecutive ( back-to-back) cycles clomiphene citrate; excessive over-exposure to produced or administered androgens( e.g., testosterone, androstenedione) particularly in women with diminished ovarian reserve ( DOR) or polyendocrine metabolic ovarian syndrome (PMOS); extensive adenomyosis (relatively infrequent); and multiple uterine fibroids that compromise uterine blood flow.

Recognizing that reduced uterine blood flow contributes to many cases of thin endometrium, we introduced the vaginal administration of sildenafil (Viagra) in 1996 as a means of selectively increasing blood flow to the basal endometrium. Vaginal administration achieves high local concentrations while minimizing systemic side effects and has proven helpful in many women whose endometrium remains estrogen responsive. Unfortunately, no treatment can reliably restore endometrial function when the basal layer has sustained irreversible damage.

2. BIOLOGIC IMPLANTATION DYSFUNCTION

Not all implantation failure can be seen on ultrasound or hysteroscopy.

Many women have perfectly normal uterine cavities, an adequately developed endometrium, and embryos of excellent quality, yet implantation repeatedly fails. In such cases, the problem frequently lies not in the anatomy of the uterus but in its biology…..particularly in the remarkably sophisticated immune system that governs whether an embryo is accepted or rejected.

Contrary to popular belief, the uterus is not simply a passive incubator awaiting the arrival of an embryo. It is an immunologically active organ whose primary responsibility is to distinguish between tissues that should be accepted and those that should be eliminated. Because every embryo contains genetic material contributed by both parents, it is biologically unique. Successful implantation therefore depends upon the establishment of a carefully regulated immunologic dialogue between the embryo and the maternal endometrium.

When that dialogue is disrupted, implantation may fail before pregnancy has even begun, or the pregnancy may end in miscarriage soon after implantation. This phenomenon is known as Immunologic Implantation Dysfunction (IID) , in my opinion, remains one of the most overlooked causes of repeated IVF failure and recurrent pregnancy loss.

A. Autoimmune Implantation Dysfunction

During the implantation window, more than 70% of the immune cells present within the endometrium are natural killer (NK) cells and T lymphocytes. These cells are not harmful by nature. In fact, they are essential for normal implantation because they regulate trophoblast invasion, placental development, and remodeling of the maternal blood vessels that ultimately nourish the growing fetus.

The problem arises when these cells become excessively “activated” .

Activated NK cells produce excessive amounts of pro-inflammatory TH-1 cytokines that induce programmed cell death (apoptosis) within trophoblastic tissue, limiting placental development and preventing successful implantation. At the same time, protective TH-2 cytokines, which normally facilitate implantation, become relatively deficient. The result is an imbalance that favors reproductive failure.

This excessive immune activation has been associated with “unexplained” infertility, repeated implantation failure, recurrent pregnancy loss, endometriosis, thyroid autoimmunity, and several systemic autoimmune diseases including lupus erythematosus, rheumatoid arthritis, scleroderma, and dermatomyositis.

One of the greatest misconceptions in reproductive immunology is that simply measuring the number of NK cells in the blood provides useful information…... It does not! The issue is not how many NK cells are present…..rather, it is whether they are activated. A woman may have relatively few circulating NK cells while those present within the uterus are highly activated and capable of disrupting implantation. This is something that is sometimes seen in women with endometriosis where the concentration of NK cells in the blood is often reduced while there is NK cell activation ( NKa). Failure to recognize this phenomenon can often lead to an incorrect conclusion that there is no underlying IID.

For this reason, assessment of NK-cell activity ( NKa) rather than NK-cell number is essential. In my opinion, the K-562 target-cell cytotoxicity assay remains the most clinically useful method of evaluating NK-cell activation because even though it does not measure uterine in case cell activity directly, closely correlates with it , providing a reliable measure of the functional ability of NK cells to destroy target cells (rather than simply counting them).

ther autoimmune markers also deserve careful evaluation. Women with antiphospholipid antibodies (APA) frequently experience implantation failure because these antibodies interfere with early trophoblastic development. More than three decades ago, we introduced low-dose heparin therapy for appropriately selected APA-positive patients and demonstrated that preventing this immune-mediated interference could significantly improve implantation. Today, low-molecular-weight heparins such as Lovenox® and Clexane® have largely replaced unfractionated heparin because they are more convenient and equally effective.

Similarly, thyroid autoimmunity deserves special attention. Thyroid peroxidase (TPO) and thyroglobulin antibodies are frequently encountered in women with infertility and recurrent pregnancy loss, even when thyroid hormone levels are completely normal.

Importantly, these antibodies themselves are probably not the direct cause of reproductive failure. Rather, they often serve as markers identifying women in whom abnormal NK-cell activation and cytotoxic T-cell activity are present. Approximately half of women with thyroid autoimmunity (regardless of the absence or presence of thyroid endocrine dysregulation) demonstrateaccompanying NKa . As such, these patients will often benefit from selective immunomodulatory therapy.

B. Alloimmune Implantation Dysfunction

A second—and even less widely recognized form of IID occurs when the maternal immune system fails to recognize the embryo as sufficiently genetically different from itself.

Under normal circumstances, the embryo inherits one set of genes from the mother and one from the father. This genetic difference allows the maternal immune system to recognize the embryo appropriately and establish the immune tolerance required for implantation.

Occasionally, however, both partners share similar DQ alpha/HLA genetic patterns. In these uncommon situations, the maternal immune system may fail to establish normal immune tolerance, resulting instead in progressive activation of NK cells and cytotoxic T lymphocytes.

The consequences can be devastating.

Initially, implantation may still occur, allowing one or more normal pregnancies. However, with repeated exposure to genetically similar embryos, immune activation may progressively increase. Women may first experience recurrent miscarriage, followed by repeated implantation failure and, ultimately, what appears to be “unexplained” secondary infertility as pregnancies fail before they are even clinically recognized.

Diagnosis requires demonstrating both significant DQ alpha/HLA matching and evidence of abnormal immune activation. Genetic matching alone does not cause reproductive failure. It is the associated activation of the uterine immune system that produces implantation dysfunction.

Partial genetic matching generally responds well to carefully timed immunotherapy, with transfer of a single embryo to minimize immune stimulation. Complete genetic matching, although fortunately very uncommon, presents a much greater challenge. In selected cases, gestational surrogacy may ultimately provide the most realistic opportunity for achieving a healthy live birth.

Treatment of Immunologic Implantation Dysfunction

The successful treatment of IID requires correcting the underlying immune imbalance rather than simply repeating IVF.

The cornerstone of therapy in appropriately selected patients is immunomodulation. Intralipid (IL) infusion, administered approximately 10–14 days before embryo transfer and repeated during early pregnancy when indicated, has become the preferred treatment because it is effective, relatively inexpensive, and associated with remarkably few side effects. When combined with carefully selected corticosteroid therapy, it can reduce excessive NK-cell activation and restore a more favorable balance between pro-inflammatory TH-1 and implantation-promoting TH-2 cytokines.

Timing is critical. Neither Intralipid nor intravenous immunoglobulin (IVIg) immediately suppresses already activated NK cells. Instead, these treatments influence the development of new NK cells over the ensuing two weeks. Administering treatment immediately before embryo transfer therefore misses the biologic window during which immune modulation is most effective.

Patients with antiphospholipid antibodies (APA) frequently benefit from the addition of low-molecular-weight heparin throughout treatment and early pregnancy. Conversely, baby aspirin has not consistently demonstrated benefit in implantation dysfunction and, in some circumstances, may increase bleeding without improving reproductive outcome.

Although biologic agents such as Enbrel® and Humira® suppress certain inflammatory pathways, convincing evidence supporting their routine use in IVF remains limited. Because TH-1 cytokines also play important physiologic roles during early implantation, indiscriminate suppression may prove counterproductive

The key principle is that treatment must be individualized. Immunotherapy should never be administered simply because IVF has failed. It should be reserved for women in whom careful clinical evaluation and appropriate laboratory testing demonstrate a genuine immunologic disorder likely to impair implantation.

The Take-Home Message

The greatest advances in IVF over the past four decades have focused on producing better embryos, and those advances have transformed reproductive medicine. Yet creating a healthy embryo represents only half of the equation.

The embryo is the seed.

The uterus is the soil.

No matter how healthy the seed may be, it cannot flourish unless the soil is structurally normal, biologically receptive, and immunologically accepting.

When repeated IVF failure occurs despite the transfer of good-quality or chromosomally normal embryos, it is no longer sufficient simply to question embryo quality. It becomes essential to ask a different question:

Could implantation dysfunction be the missing diagnosis?

For many couples, the answer to that question changes everything. Rather than accepting repeated failure as inevitable or prematurely moving to egg donation or gestational surrogacy, careful evaluation of uterine anatomy, endometrial receptivity, and reproductive immunology may identify a correctable cause of reproductive failure.

The future of reproductive medicine lies not only in producing better embryos but in developing a deeper understanding of the remarkable biological dialogue between the embryo and the uterus. Only by giving equal attention to both the seed and the soil can we truly maximize the opportunity for successful implantation, a healthy pregnancy, and ultimately the birth of a healthy child