1. The nature of biochemical pregnancy: the natural mechanism of early survival of the fittest

Definition: Biochemical pregnancy refers to the phenomenon in which an embryo secretes hCG (positive blood/urine test) but stops developing before forming a gestational sac.
Core characteristics:
High incidence: The incidence rate is about 30% in natural pregnancies and 12%-30% in vitro cycles
Differences from abortion: No need for uterine curettage, less damage to the uterus, and belongs to natural elimination in the early stage of the embryo
Root cause: More than 50% result from chromosomal aneuploidy abnormalities (such as trisomy 16 and 22).
Key cognition: Biochemistry is the body's active screening mechanism for abnormal embryos, not treatment failure.
Can the second and third generation test tube (PGT) avoid biochemistry? Technical value and limitations

Advantages of PGT technology
Screening scope: Biopsy of blastocyst trophoblast cells and detect 23 pairs of chromosomes for aneuploidy (such as Down syndrome related to trisomy 21)
Applicable population: Elderly people (35 years old), repeated biochemical/abortion, and balanced chromosome translocation of couples can reduce the abortion rate caused by chromosome abnormalities by 60%.
Technical limitations (reasons why biochemistry cannot be avoided 100%)
1. Chimeric error:
Chromosomal inconsistency of up to 2% between trophoblastic cells (test samples) and inner cell mass (developed into the fetus), resulting in a risk of false negatives/positives
2. Detection blind area:
Unable to cover gene point mutations and epigenetic abnormalities
Low detection rate of sex chromosome (X/Y) abnormalities
3. Clinical data:
The biochemical rate of PGT passing embryos was not significantly different from that of unscreened embryos, but significantly reduced the risk of abortion after 12 weeks of pregnancy (Level of Evidence: Level B).
Conclusion: PGT is an important tool for high-risk groups, but it is an "absolute antidote" for non-biochemical pregnancies.
3. The neglected key factor: endometrial receptivity

Influence mechanism and response
1. Intimal thickness and shape:
The< biochemical risk doubles when the thickness is 7mm, and the ideal thickness is 8-12mm
Three-line intima (type A) is suitable for receptivity, while type C (homogeneous and highly echoic) requires intervention
2. Planting window shift:
About 30% of patients deviate from the standard cycle of implantation window (WOI), allowing the implantation opportunity to be accurately located through endometrial receptivity testing (ERA)
3. Interventions:
·Hysteroscopic treatment of polyps/adhesions
·Estrogen improves intimal blood flow and progesterone optimizes progesterone support.
Special challenges to the emission cycle
High estrogen levels after hyperstimulation can lead to:
·Abnormal uterine peristaltic waves interfere with embryo positioning
·Gene expression in the intima is disturbed and receptivity is reduced.
Countermeasures: Give priority to frozen embryo transfer to avoid endocrine fluctuations after promoting expulsion.
4. Immunization and coagulation: potential triggers in controversy

Abnormal indicators to pay attention to
·Autoantibodies: positive for anti-phospholipid antibodies and antinuclear antibodies (causing prethrombotic conditions and blocking the recasting of placental blood vessels)
·Coagulation function: Hypercoagulability (such as protein S deficiency) causes microthrombus in decidua, hindering the nutrient supply of the embryo.
Intervention strategy (Level of Evidence: Level C)
·Low molecular weight heparin + low-dose aspirin (to improve uterine perfusion)
·Immunosuppressants (such as prednisone) are used to identify patients with autoimmune diseases.
ˇNote: Non-universal solution! The drug needs to be used after joint evaluation by the Department of Rheumatology and Immunology.
5. Systematic coping strategies: from attribution to action

List of must-check items

6. Key summary for expectant parents

1. Treat biochemistry rationally:
Single biochemistry is a natural screening process and does not require excessive treatment; repeated biochemistry (≥2 times) requires comprehensive screening
2. Technology selection logic:
Non-elderly people with no chromosomal abnormalities: first-generation/second-generation test tube + frozen embryo transfer is enough
Elderly people/genetically at risk: PGT+ personalized intimal preparation is the preferred combination
3. Focus on doctor-patient collaboration:
Trust the attending doctor and avoid frequent changes in plan
Record menstrual cycles and medication reactions to help accurately review.

Ultimate belief: Biochemistry is the signpost on the road to success, not the end-adjusting the soil (inner membrane), optimizing seeds (embryos), eliminating hidden dangers (immunity), and eventually reaching the moment of "life landing".