Opening: Perspective on the causes of failure cases
Clinic case: A 36-year-old woman, AMH 1.2 ng/mL, with a history of two previous transfers of Day5 blastocysts (4AA, 4AB) both failing to implant. Endometrial thickness before transfer was 8.2mm, morphology normal, hormone replacement therapy cycle protocol. Male partner's semen analysis normal. β-hCG was <1 mIU/mL after both transfers. Patient's chief complaint: "The embryo quality was good, why didn't it implant?"
This is a typical consultation scenario for recurrent implantation failure (RIF). In reproductive clinics, similar cases account for approximately 15%–25% of total IVF cycles. To answer "What are the reasons for IVF failure in China?", it is necessary to break down the factors from four dimensions: embryo, uterus, maternal, and technology. It is also crucial to distinguish between first failure and recurrent failure, as the weight of causes differs significantly between these situations.
I. Core Classification of Reasons for IVF Failure
According to multi-center clinical data from the Chinese assisted reproduction industry, the main reasons for not achieving a live birth after IVF/ICSI cycles can be summarized into the following four categories:
| Category | Specific Factors | Estimated Clinical Proportion |
|---|---|---|
| Embryo Factors | Chromosomal aneuploidy, embryo developmental arrest, mitochondrial dysfunction, fragmentation rate >20% | 50%–60% |
| Uterine Factors | Decreased endometrial receptivity, intrauterine adhesions, chronic endometritis, endometrial polyps/fibroids (submucosal) | 20%–30% |
| Maternal Factors | Thyroid dysfunction, hyperprolactinemia, positive antiphospholipid antibodies, abnormal NK cells, vitamin D deficiency, metabolic syndrome | 10%–20% |
| Technical/Laboratory Factors | Embryo culture environment, transfer catheter operation, embryo-endometrial synchrony error, laboratory quality control fluctuations | 5%–10% |
It should be noted that the above proportions vary depending on patient age, etiology composition, and center technical protocols. For women over 38 years old, the proportion of embryo chromosomal abnormalities may rise to 70%–80%.
II. Why Do These Factors Lead to Failure?
2.1 Embryo Chromosomal Abnormalities – The Most Common Single Factor
During the meiotic division of human oocytes, the probability of chromosome non-disjunction increases significantly with age. A blastocyst that appears "morphologically good" still has a 30%–50% probability of being chromosomally aneuploid (PGT-A data). Such embryos can form blastocysts and may even have a normal developmental rate, but after transfer, they either fail to implant or result in biochemical pregnancy or spontaneous miscarriage in early pregnancy.
Why can't morphological grading completely replace genetic screening? Because the "appearance" of the embryo is determined by the trophectoderm cells, and the chromosomal status of the inner cell mass (which will develop into the fetus) is not always consistent with the trophectoderm. This is why doctors recommend considering PGT-A for patients with recurrent implantation failure.
2.2 Endometrial Receptivity – The "Soil" Problem for Implantation
Endometrial receptivity refers to the ability of the endometrium to accept embryo implantation during a specific time window (window of implantation). Mechanisms of impaired receptivity include:
- Chronic Endometritis (CE): Plasma cell infiltration leads to an imbalance of local inflammatory factors, interfering with implantation. The detection rate of CE in RIF patients can reach 30%–40%.
- Endometrial Microbiome Dysbiosis: Decreased proportion of Lactobacillus and increased pathogenic bacteria affect the endometrial immune microenvironment.
- Thin Endometrium: Implantation rates decrease significantly when thickness is <7mm, but thickness is not the only indicator; endometrial blood flow and morphology (triple-line sign) are equally important.
2.3 Maternal Endocrine and Immune Factors
Thyroid function (TSH >2.5 mIU/L), hyperprolactinemia, and vitamin D deficiency (<30 ng/mL) are all associated with implantation failure. Among immune factors, positive antiphospholipid antibodies (ACA, LA, β2-GP1), elevated natural killer (NK) cell activity, and abnormal autoantibodies may lead to recurrent failure by affecting maternal-fetal interface immune tolerance.
III. How Do Doctors View "IVF Failure"?
Clinical Decision Logic: Faced with a single failure, doctors usually do not immediately define it as "recurrent implantation failure." Instead, they first distinguish whether it is an "embryo problem" or a "uterine/maternal problem." If there is only one failed transfer and the risk of embryo aneuploidy is high (female age ≥38 years or history of chromosomal abnormality pregnancy), the doctor may prioritize recommending PGT-A.
For two or more failed transfers of good-quality embryos without implantation, a RIF evaluation process is initiated clinically: Hysteroscopy + Endometrial biopsy (CD138 testing) + Thyroid function + Antiphospholipid antibodies + Thrombophilia screening + Vitamin D testing. Some centers may add ERA (Endometrial Receptivity Array) to determine window of implantation displacement.
What doctors focus on is not the "failure" itself, but "why did failure occur in this patient, in this cycle, with this embryo?" Individualized attribution is the basis for formulating the next plan.
IV. Differences in the Weight of Failure Causes Across Age Groups
| Age Group | Main Causes of Failure (by weight) | Clinical Strategy Focus |
|---|---|---|
| ≤34 years | Uterine factors (endometritis, polyps, adhesions) > Embryo factors > Immune factors | Prioritize investigation of uterine pathology, perform hysteroscopy if necessary; consider ERA |
| 35–39 years | Embryo chromosomal abnormalities > Uterine factors > Endocrine/Immune factors | PGT-A (if ≥2 failures); simultaneously assess endometrial receptivity |
| ≥40 years | Embryo aneuploidy (70%–80%) > Oocyte mitochondrial function > Endometrial factors | PGT-A + Mitochondrial DNA content assessment; consider oocyte donation |
Age is the most critical variable affecting the weight of failure causes. Women under 35 may still achieve live birth through maternal repair mechanisms even after transferring aneuploid embryos, but this repair capacity significantly declines after age 40.
V. Most Easily Overlooked Details
5.1 Chronic Endometritis (CE) – The Silent Implantation Killer
CE usually has no obvious symptoms; increased vaginal discharge, mild abdominal pain, or prolonged menstruation are easily overlooked. However, CD138-positive plasma cell infiltration alters the endometrial gene expression profile. A retrospective study including 236 RIF patients showed that after antibiotic treatment for CE, the clinical pregnancy rate in subsequent transfers increased from 18.5% to 41.2%.
Note: Routine ultrasound cannot diagnose CE; diagnosis relies on hysteroscopy + endometrial biopsy (CD138 immunohistochemistry). If recurrent transfer failures have occurred without hysteroscopy, this is an easily missed examination.
5.2 Thyroid Function – Ideal TSH Range
Even if TSH is within the normal range (0.5–4.5 mIU/L), for RIF patients, most reproductive centers set the target value at <2.5 mIU/L. A meta-analysis showed that women with TSH between 2.5–4.0 mIU/L have an approximately 12% reduction in implantation rate. If combined with positive thyroid peroxidase antibodies (TPOAb), even with normal TSH, levothyroxine intervention may be needed.
5.3 Vitamin D Levels
Vitamin D receptors are widely present in the endometrium and immune cells. Serum 25-hydroxyvitamin D <30 ng/mL is associated with decreased implantation rates and increased miscarriage rates. In northern regions, with insufficient winter sunlight, the incidence of vitamin D deficiency can exceed 60%. This test is inexpensive (approximately 80–120 RMB) but is often overlooked.
VI. Most Common Pitfalls
Pitfall 1: "Good embryo grade means no problem" – Morphological grading and chromosomal status are not the same. A 4AA blastocyst still has about a 35% probability of being abnormal (at female age 38).
Pitfall 2: "PGT-A can solve all failures" – PGT-A can only screen for chromosomally euploid embryos but cannot address endometrial receptivity, immune, or endocrine issues. If a patient has both CE and thyroid abnormalities, even transferring a euploid embryo, the implantation rate remains limited.
Pitfall 3: "Recurrent failure is the woman's problem" – In fact, male factors (sperm chromosomal structural abnormalities, sperm DNA fragmentation rate >30%, Y chromosome microdeletions, etc.) account for about 10%–15% of RIF cases. Elevated sperm DNA fragmentation rate is associated with embryo developmental arrest and decreased blastocyst formation rate.
Pitfall 4: "Strict bed rest after transfer" – There is no evidence that bed rest for more than 4 hours improves implantation rates; it may instead increase the risk of thrombosis. Normal activity, avoiding strenuous exercise, is sufficient.
VII. Key Examination Indicators and Their Clinical Significance
After IVF failure, doctors will order a series of investigations. Below is an interpretation of the most commonly used indicators:
| Test Item | Normal/Ideal Range | Clinical Significance When Abnormal |
|---|---|---|
| AMH | ≥1.0 ng/mL | Reflects ovarian reserve; AMH <0.5 ng/mL indicates low follicle count, potentially insufficient oocyte yield, limiting embryo selection |
| TSH | 0.5–2.5 mIU/L (RIF target) | >2.5 mIU/L associated with decreased implantation rate; intervention needed if TPOAb positive |
| Vitamin D | ≥30 ng/mL | <20 ng/mL indicates deficiency, associated with implantation failure and increased miscarriage rate |
| Antiphospholipid Antibodies (ACA/LA/β2-GP1) | Negative | Positive indicates antiphospholipid syndrome, requires anticoagulation therapy; associated with recurrent implantation failure and recurrent miscarriage |
| NK Cell Activity (Peripheral Blood) | <30% | Elevated activity may suggest enhanced immune attack at the maternal-fetal interface, but clinical controversy exists; should be combined with other indicators |
| Sperm DNA Fragmentation Index (DFI) | <30% | DFI >30% associated with embryo developmental arrest, decreased blastocyst formation rate, and increased miscarriage rate |
How to determine which tests to prioritize? For first failure in patients ≤37 years old, TSH, vitamin D, and antiphospholipid antibodies are usually rechecked first, along with a recommendation for hysteroscopy. For patients ≥38 years old or with a history of chromosomal abnormality pregnancy, embryo genetic analysis (PGT-A or chromosomal microarray analysis of miscarriage tissue) is prioritized.
VIII. Frequently Asked Questions
Q1: How long after IVF failure can the next transfer be performed?
If no ovarian hyperstimulation syndrome (OHSS) occurred and there are no complications from uterine procedures, an interval of 1–2 natural cycles is usually recommended to allow the endometrium to fully recover. If hysteroscopy or biopsy was performed, it is advisable to wait for the next menstrual cycle. If there was a pregnancy (biochemical or miscarriage), it is recommended to wait until hCG returns to normal before starting preparation, typically 1–2 months.
Q2: Is ERA meaningful for recurrent implantation failure?
When is it suitable? If embryo chromosomal abnormalities (normal PGT-A), uterine pathology, and endocrine factors have been ruled out, and failure persists, ERA can be considered. ERA analyzes endometrial gene expression to determine if the window of implantation is displaced (advanced or delayed). Approximately 20%–30% of RIF patients have window of implantation displacement.
When is it not suitable? If untreated chronic endometritis, thyroid dysfunction, or positive antiphospholipid antibodies exist, these issues should be addressed first, as they can affect the value of ERA.
Q3: Can embryos with high fragmentation rate be transferred?
Embryos with a fragmentation rate >20% have significantly reduced implantation potential. However, embryos with fragmentation rate <15% that can form blastocysts still have a reasonable probability of live birth. Laboratories typically consider fragmentation rate <10% as good, 10%–20% as transferable, and >20% as observation or discard. If all embryos have high fragmentation rates, it is necessary to investigate sperm DFI, maternal oxidative stress status, and laboratory culture conditions.
Q4: What can be done for a thin endometrium?
Implantation rates are limited when endometrial thickness is <7mm. Management options include: prolonging estrogen use (8–12 days), adding low-dose aspirin, intrauterine infusion of G-CSF or PRP (platelet-rich plasma), using GnRH agonist cycles, etc. However, it is important to clarify: endometrial thickness is not the sole determining factor; endometrial blood flow, morphology, and gene expression profile also influence outcomes.
IX. Brief Overview of Differences in IVF Failure Causes Across Countries
Although the biological basis of failure causes is similar, differences in patient demographics and clinical practices across countries lead to variations in the weight of causes:
- China: Due to the rising proportion of advanced maternal age (≥35 years) seeking fertility, the proportion of failures caused by embryo chromosomal abnormalities is higher than in European and American countries. Additionally, the detection rate of chronic endometritis in the Chinese RIF population (approximately 35%–40%) is higher than in some Western centers (approximately 20%–25%), possibly related to a higher history of intrauterine procedures and cesarean sections.
- USA/Europe: PGT-A is used more widely, so the proportion of "non-implantation" due to embryo aneuploidy is relatively lower, while the proportion of endometrial receptivity and immune factors is relatively higher. Furthermore, some European centers have stricter limits on the number of embryos transferred (primarily single embryo transfer), so "multiple pregnancy reduction-related failures" are less common.
X. Doctor's Advice
Regarding next steps after IVF failure:
- First failure: Review cycle protocol, embryo grading, and endometrial condition. If age ≤37 years, recommend hysteroscopy to rule out uterine pathology; check TSH, vitamin D, and antiphospholipid antibodies. If age ≥38 years, discuss the necessity of PGT-A with the doctor.
- Two or more failures (RIF): Initiate standard RIF investigation protocol (hysteroscopy + CD138, endocrine, immune, thrombophilia screening). Simultaneously consider genetic analysis of remaining embryos or previous miscarriage tissue. If all tests are normal, discuss ERA and window of implantation adjustment.
- Precautions: It is not recommended to blindly change hospitals or doctors without identifying the cause. Each failure should serve as a basis for "attribution analysis," not simply repeating the same protocol. Additionally, psychological stress itself can affect endometrial receptivity through hormones like cortisol; appropriate psychological counseling or stress management is recommended.
Risk Reminder: The content of this article is based on general clinical knowledge in the assisted reproduction field. Specific diagnosis and treatment plans should be discussed with your primary reproductive physician. Laboratory conditions, operational habits, and medication protocols vary among different reproductive centers; attribution analysis must be combined with actual circumstances. No success rates are promised, and this does not constitute medical advice.
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