When it comes to reproduction, humans face challenges compared to other mammals. A significant number of fertilized eggs in humans do not result in live births, with up to 75% failing to develop, and around 30% of pregnancies ending within the first 10 weeks  (first trimester). Recurrent pregnancy loss (RPL) refers to two or more consecutive failed pregnancies, which is relatively rare, affecting less than 5% of women for two losses and only 1% for three or more losses. Understanding the causes of pregnancy loss and finding solutions is crucial for those affected. This article aims to explain the different types of pregnancy loss and shed light on potential causes.

Types of Pregnancy Loss

Pregnancy loss can occur at various stages, leading to different classifications:

  1. Early Pregnancy Loss: Also known as a miscarriage, this typically happens in the first trimester. Early pregnancy losses are usually sporadic, not recurring. In over 70% of cases, these losses are due to chromosomal abnormalities in the embryo, where there are more or fewer than the normal 46 chromosomes. Therefore, they are not likely to be repetitive.
  2. Late Pregnancy Loss: Late pregnancy losses occur after the first trimester (12th week) and are less common (1% of pregnancies). They often result from anatomical abnormalities in the uterus or cervix. Weakness in the cervix, known as cervical incompetence, is a frequent cause. Other factors include developmental abnormalities of the uterus, uterine fibroid tumors, intrauterine growth retardation, placental abruption, premature rupture of membranes, and premature labor.

Causes of Recurrent Pregnancy Loss (RPL)

Recurrent pregnancy loss refers to multiple consecutive miscarriages. While chromosomal abnormalities are a leading cause of sporadic early pregnancy losses, RPL cases are mostly attributed to non-chromosomal factors. Some possible causes include:

  1. Uterine Environment Problems: Issues with the uterine environment can prevent a normal embryo from properly implanting and developing. These problems may include inadequate thickening of the uterine lining, irregularities in the uterine cavity (such as polyps, fibroid tumors, scarring, or adenomyosis), hormonal imbalances (progesterone deficiency or luteal phase defects), and deficient blood flow to the uterine lining.
  2. Immunologic Implantation Dysfunction (IID): IID is a significant cause of RPL, contributing to 75% of cases where chromosomally normal embryos fail to implant. It involves the immune system’s response to pregnancy, which can interfere with successful implantation.
  3. Blood Clotting Disorders: Thrombophilia, a hereditary clotting disorder, can disrupt the blood supply to the developing fetus, leading to pregnancy loss.
  4. Genetic and Structural Abnormalities: Genetic abnormalities are rare causes of RPL, while structural chromosomal abnormalities occur infrequently (1%). Unbalanced translocation, where part of one chromosome detaches and fuses with another, can lead to pregnancy loss. Studies also suggest that damaged sperm DNA can negatively impact fetal development and result in miscarriage.


Autoimmune IID: Here, an immunologic reaction is produced by the individual to his/her body’s own cellular components. The most common antibodies that form in such situations are APA and antithyroid antibodies (ATA). But it is only when specialized immune cells in the uterine lining, known as cytotoxic lymphocytes (CTL) and natural killer (NK) cells, become activated and start to release an excessive/disproportionate amount of TH-1 cytokines that attack the root system of the embryo, that implantation potential is jeopardized. Diagnosis of such activation requires highly specialized blood test for cytokine activity that can only be performed by a handful of reproductive immunology reference laboratories in the United States.

Alloimmune IID, (i.e., where antibodies are formed against antigens derived from another member of the same species), is believed to be a common immunologic cause of recurrent pregnancy loss. Autoimmune IID is often genetically transmitted. Thus, it should not be surprising to learn that it is more likely to exist in women who have a family (or personal) history of primary autoimmune diseases such as lupus erythematosus (LE), scleroderma or autoimmune hypothyroidism (Hashimoto’s disease), autoimmune hyperthyroidism (Grave’s disease), rheumatoid arthritis, etc. Reactionary (secondary) autoimmunity can occur in conjunction with any medical condition associated with widespread tissue damage. One such gynecologic condition is endometriosis.

Since autoimmune IID is usually associated with activated NK and T-cells from the outset, it usually results in such very early destruction of the embryo’s root system that the patient does not even recognize that she is pregnant. Accordingly, the condition usually presents as “unexplained infertility” or “unexplained IVF failure” rather than as a miscarriage.

Alloimmune IID, on the other hand, usually starts off presenting as unexplained miscarriages (often manifesting as RPL). Over time as NK/T cell activation builds and eventually becomes permanently established the patient often goes from RPL to “infertility” due to failed implantation. RPL is more commonly the consequence of alloimmune rather than autoimmune implantation dysfunction. However, regardless, of whether miscarriage is due to autoimmune or alloimmune implantation dysfunction the final blow to the pregnancy is the result of activated natural killer cells (NKa) and cytotoxic lymphocytes (CTL B) in the uterine lining that damage the developing embryo’s “root system” (trophoblast) so that it can no longer sustain the growing conceptus.

This having been said, it is important to note that autoimmune IID is readily amenable to reversal through timely, appropriately administered, selective immunotherapy, and alloimmune IID is not. It is much more difficult to treat successfully, even with the use of immunotherapy. In fact, in some cases the only solution will be to revert to selective immunotherapy plus using donor sperm (provided there is no “match” between the donor’s DQa profile and that of the female recipient) or alternatively to resort to gestational surrogacy. 


In the past, women who miscarried were not evaluated thoroughly until they had lost several pregnancies in a row. This was because sporadic miscarriages are most commonly the result of embryo numerical chromosomal irregularities (aneuploidy) and thus not treatable. However, a consecutive series of miscarriages points to a repetitive cause that is non-chromosomal and is potentially remediable. Since RPL is most commonly due to a uterine pathology or immunologic causes that are potentially treatable, it follows that early chromosomal evaluation of products of conception could point to a potentially treatable situation. Thus, I strongly recommend that such testing be done in most cases of miscarriage. Doing so will avoid a great deal of unnecessary heartache for many patients.

Establishing the correct diagnosis is the first step toward determining effective treatment for couples with RPL. It results from a problem within the pregnancy itself or within the uterine environment where the pregnancy implants and grows. Diagnostic tests useful in identifying individuals at greater risk for a problem within the pregnancy itself include:

  • Karyotyping (chromosome analysis) both prospective parents
  • Assessment of the karyotype of products of conception derived from previous miscarriage specimens
  • Ultrasound examination of the uterine cavity after sterile water is injected or sonohysterogram, fluid ultrasound, etc.)
  • Hysterosalpingogram (dye X-ray test)
  • Hysteroscopic evaluation of the uterine cavity
  • Full hormonal evaluation (estrogen, progesterone, adrenal steroid hormones, thyroid hormones, FSH/LH, etc.)
  • Immunologic testing to include Antiphospholipid antibody (APA) panel
  • Antinuclear antibody (ANA) panel
  • Antithyroid antibody panel (i.e., antithyroglobulin and antimicrosomal antibodies)
  • Reproductive immunophenotype
  • Natural killer cell activity (NKa) assay (i.e., K562 target cell test)
  • Alloimmune testing of both the male and female partners


Treatment for Anatomic Abnormalities of the Uterus

This involves restoration through removal of local lesions such as fibroids, scar tissue, and endometrial polyps or timely insertion of a cervical cerclage (a stitch placed around the neck of the weakened cervix) or the excision of a uterine septum when indicated. Treatment of Thin Uterine Lining: A thin uterine lining has been shown to correlate with compromised pregnancy outcome. Often this will be associated with reduced blood flow to the endometrium. Such decreased blood flow to the uterus can be improved through treatment with sildenafil and possibly aspirin.

Sildenafil (Viagra) Therapy

Viagra has been used successfully to increase uterine blood flow. However, to be effective it must be administered starting as soon as the period stops up until the day of ovulation and it must be administered vaginally (not orally). Viagra in the form of vaginal suppositories given in the dosage of 25 mg four times a day has been shown to increase uterine blood flow as well as thickness of the uterine lining.

To date, we have seen significant improvement of the thickness of the uterine lining in about 70% of women treated. Successful pregnancy resulted in 42% of women who responded to the Viagra. It should be remembered that most of these women had previously experienced repeated IVF failures. Use of Aspirin: This is an anti-prostaglandin that improves blood flow to the endometrium. It is administered at a dosage of 81 mg orally, daily from the beginning of the cycle until ovulation. 

Treating Immunologic Implantation Dysfunction with Selective Immunotherapy

Modalities such as intralipid (IL), intravenous immunoglobulin-G (IVIG),  heparinoids (Lovenox/Clexane), and corticosteroids (dexamethasone, prednisone, prednisolone) can be used in select cases depending on autoimmune or alloimmune dysfunction.

The Use of IVF in the Treatment of RPL

In the following circumstances, IVF is the preferred option: When in addition to a history of RPL, another standard indication for IVF (e.g., tubal factor, endometriosis, and male factor infertility) is superimposed and in cases where selective immunotherapy is needed to treat an immunologic implantation dysfunction.  The reason for IVF being a preferred approach when immunotherapy is indicated is that in order to be effective, immunotherapy needs to be initiated well before spontaneous or induced ovulation. Given the fact that the anticipated birthrate per cycle of COS with or without IUI is at best about 15%, it follows that short of IVF, to have even a reasonable chance of a live birth, most women with immunologic causes of RPL would need to undergo immunotherapy repeatedly, over consecutive cycles.

Conversely, with IVF, the chance of a successful outcome in a single cycle of treatment is several times greater and, because of the attenuated and concentrated time period required for treatment, IVF is far safer and thus represents a more practicable alternative Since embryo aneuploidy is a common cause of miscarriage, the use of preimplantation genetic screening/ testing (PGS/T), with tests such as next generation gene sequencing (NGS), can provide a valuable diagnostic and therapeutic advantage in cases of RPL. PGS/T requires IVF to provide access to embryos for testing.

There are a few cases of intractable alloimmune dysfunction due to absolute DQ alpha gene matching ( where there is a complete genotyping match between the male and female partners) where Gestational Surrogacy or use of donor sperm could represent the only viable recourse, other than abandoning treatment altogether and/or resorting to adoption. Other non-immunologic factors such as an intractably thin uterine lining or severe uterine pathology might also warrant that last resort consideration be given to gestational surrogacy.


Understanding the causes of pregnancy loss is crucial for individuals experiencing recurrent miscarriages. While chromosomal abnormalities are a common cause of sporadic early pregnancy losses, other factors such as uterine environment problems, immunologic implantation dysfunction, blood clotting disorders, and genetic or structural abnormalities can contribute to recurrent losses. By identifying the underlying cause, healthcare professionals can provide appropriate interventions and support to improve the chances of a successful pregnancy. The good news is that if a couple with RPL is open to all of the diagnostic and treatment options referred to above, a live birthrate of 70%–80% is ultimately achievable.

Still searching for “miscarriage specialist near me”? Look no further. At Sher Fertility Solutions, our renowned recurrent miscarriage specialists are ready to provide personalized, compassionate care. We offer comprehensive evaluations and tailored treatment plans to uncover and address the root causes of your recurrent miscarriages. Book a consultation with us to get started.