Implantation Failure: Causes, Risk Factors, Prevention, and Treatment Options

Implantation failure (failed attachment of blastocyst to receptive endometrium) accounts for ~50–75% of early pregnancy losses — most before clinical recognition.

Etiologic Categories

1. Embryonic Factors (Majority):
   • Aneuploidy (↑ with maternal age: 20% at 30 → 80% at 42).
   • Mosaicism, genetic mutations, metabolic stress.
2. Endometrial Factors:
   • Structural: Polyps, submucosal fibroids, adhesions (Asherman's), septum, thin lining (<7 mm).
   • Receptive Window Displacement: WOI (window of implantation) shift — ERA test guides personalized embryo transfer (pET).
   • Chronic Endometritis: Subclinical infection (plasma cells on biopsy) — tx: antibiotics ↑ LBR.
   • Microbiome: Lactobacillus dominance optimal; dysbiosis ↓ implantation.
3. Systemic / Immunologic:
   • Thrombophilia (APS, Factor V Leiden) — anticoagulation benefit debated.
   • Autoimmune: ANA, thyroid antibodies (TPO) — association, not proven causation.
   • NK cells / cytokines: Controversial; no validated test/treatment.
4. Hormonal: Luteal phase deficiency (progesterone ↓) — supplementation standard in ART.
5. Lifestyle: Smoking (↓ uterine perfusion, ↑ DNA damage), obesity (inflammation, endocrine disruption), alcohol, stress (HPA axis).
6. Iatrogenic: Controlled ovarian stimulation supraphysiologic estradiol → advanced endometrial maturation → asynchrony. Freeze-all + FET often superior.

Prevention & Optimization

• PGT-A (euploid embryo selection) — most effective single intervention for age-related failure.
• Hysteroscopy before ART (treat polyps, fibroids, septum, adhesions).
• Endometrial biopsy for chronic endometritis / ERA.
• Lifestyle: BMI 19–25, stop smoking, limit alcohol, stress reduction.
• Supplements: Folic acid, vitamin D, CoQ10, omega-3 — evidence variable.

Treatment Algorithms (RPL / RIF)

• RPL (≥2 losses): Karyotype parents, uterine cavity, APS panel, TSH, HbA1c.
• RIF (≥3 failed euploid transfers): ERA, chronic endometritis, immune workup (controversial), consider gestational carrier.

Individualized, evidence-based approach — not empirical "kitchen sink" protocols — maximizes success.