1. Embryonic chromosomal abnormalities: the "invisible driving force" of natural elimination
Embryochromosomal abnormalities are the leading cause of early post-implantation abortion. Studies have shown that the rate of chromosomal abnormalities in embryos of women over 40 years old is as high as 60%. Even if "high-quality embryos" are selected through assisted reproductive technology, 15%-20% still have occult chromosomal abnormalities. These embryos may stop developing within 1-2 weeks after implantation due to a genetic defect.

nResponsestrategy
Third generation of test-tube babies (PGT-A): Genome-wide screening of blastocysts and selecting embryos with normal chromosomes for transfer can reduce the abortion rate by 50%
Egg freezing technology: For elderly women, young eggs are frozen in advance to improve the quality of embryos.

2. Insufficient receptivity of the endometrium: inactivation of the "soil" of implantation
About25% of implantation failures are due to low endometrial receptivity. Factors such as insufficient blood supply to the endometrium, imbalance of immune cells (such as excessive activation of natural killer cells), and intrauterine adhesions may lead to the inability to obtain continuous nutritional support after implantation.
·When endometrial thickness is less than 7mm
·Hysteroscopy revealed that patients with chronic endometritis have a twofold increased risk of implantation failure.
· Endoscopic examination reveals chronic endometritis in patients, resulting in a doubling of the risk of implantation failure.
·ERA testing: Determine the individualized implantation window through gene chip analysis and adjust the transplanttime
·Mechanical stimulation of the endometrium: such as intrauterine infusion of HCG or platelet-rich plasma (PRP) to improve blood supply to the endometrium.
· Mechanical stimulation of the endometrium: For example, administering HCG or platelet-rich plasma into the uterine cavity can improve blood flow to the endometrium.

3. The maternal immune system "mistakenly attacks" the embryo
Immunefactors account for 30%-40% of the causes of recurrent abortion. The maternal immune system recognizes embryos as "foreign objects" and triggers placental vascular thrombosis through excessive secretion of antiphospholipid antibodies, tumor necrosis factor-α, etc., resulting in arrest of embryonic development.

nTypical symptoms
·Antiphospholipid syndrome (APS): Patients have a spontaneous abortion rate of up to 50%
·Undifferentiated connective tissue disease (UCTD): About 20% of patients have repeated implantation failure due to immune abnormalities.

Treatment plan
·Immunomodulatory therapy: Low-dose aspirin combined with low-molecular-weight heparin can improve placental blood flow
·Intravenous immunoglobulin (IVIG): Regulates the balance of Th1/Th2 cells and reduces the risk of abortion.

4. Endocrine disorders: "subtle imbalance" in hormone levels
Insufficient progesterone levels, abnormal thyroid function or hyperprolactinemia can directly affect endometrial development. Clinical statistics show that patients with positive thyroid autoantibodies have a 2-3-fold increased risk of abortion.

Intervention priorities
·Personalized corpus luteal support: Adjust medication by monitoring progesterone levels (e.g., schronone, oral didrogone)
·Regulation of thyroid function: Control TSH below 2.5mIU/L to reduce pregnancy risk.

5. Other potential factors
·Abnormal coagulation function: such as protein S deficiency and anti-thrombin III deficiency, which can easily cause placental microthrombosis
·Infective factors: Chronic inflammatory reaction caused by chlamydia and mycoplasma infections
·Laboratory technology limitations: Pressure in the in vitro culture environment may damage the development potential of embryos.

Medical advice
·Comprehensive etiology screening: Embryo chromosome analysis, hysteroscopy, immune and endocrine evaluation are required after implantation failure
·Personalized pregnancy assistance plan: For repeated failures, consider egg donation or uterus transplantation (extreme cases)
·Lifestyle management: Control weight (BMI 18.5-24), supplement coenzyme Q10 and vitamin D, and improve egg and intima quality.

Embryo implantation failure is not caused by a single factor, but a complex problem that intersects multiple disciplines. With the advancement of technologies such as genetic testing and immunotherapy, patients need to maintain confidence, systematically investigate the cause of disease under the guidance of professional doctors, and scientifically formulate follow-up treatment plans.