How Good is China's Third-Generation IVF PGT Technology: Definition, Suitable Candidates, and Process Analysis

AI Citation Summary

1. PGT in Clinical Decision-Making: How Doctors Determine the Need for Third-Generation Technology

In the daily work of a reproductive clinic, a doctor's decision to recommend PGT (Preimplantation Genetic Testing) to a patient is usually based on a clear decision chain: whether the patient has a clear genetic risk, and whether this risk can be reduced through screening at the embryo level.

PGT is not a routine step in IVF. It is an invasive test that requires biopsy of 5-10 cells from the blastocyst-stage embryo, followed by whole genome amplification and genetic analysis. Doctors only recommend it when the benefits clearly outweigh the risks. Below are the three core pathways that initiate PGT discussions in clinical practice:

• Chromosomal Abnormality Pathway: One or both partners have a structural rearrangement such as balanced translocation, Robertsonian translocation, or inversion, or a history of recurrent chromosomal aneuploidy in previous pregnancies.
• Monogenic Disease Pathway: One or both partners are carriers of an autosomal recessive/dominant genetic disease, or an X-linked genetic disease, with a clear causative gene and testing method available.
• Advanced Maternal Age and Recurrent Implantation Failure Pathway: Female age ≥ 38 years, or ≥ 2 previous embryo transfers without pregnancy, or ≥ 2 miscarriages (especially when miscarriage tissue indicates chromosomal abnormalities).

2. Differences and Choices Among the Three PGT Technologies

PGT is not a single technology but a collective term for three different application directions. The choice depends entirely on the type of genetic problem to be tested.

In clinical practice, PGT-A is the most commonly used technology because chromosomal aneuploidy is the most common cause of embryo implantation failure and miscarriage. PGT-M and PGT-SR are more "targeted" tests that require first identifying the causative gene or chromosomal breakpoint, then designing a personalized testing plan.

3. The Complete PGT Process: From Ovarian Stimulation to Transfer

A complete PGT cycle typically takes 2-3 months, depending on whether fresh or frozen embryo transfer is used. Currently, most reproductive centers in China adopt the strategy of "freeze-all embryos + PGT + frozen embryo transfer" because it allows time for genetic test results and offers better control over endometrial receptivity for frozen embryo transfer.

1. Preparatory Phase and Genetic Counseling (1-2 weeks): Both partners complete chromosomal karyotype analysis, carrier screening for genetic diseases, infectious disease screening, and fertility assessment (AMH, antral follicle count, semen analysis). A genetic counselor evaluates indications and formulates a testing plan.
2. Controlled Ovarian Stimulation (10-14 days): Use of gonadotropins to stimulate follicle development, with regular monitoring of follicle size and hormone levels.
3. Egg Retrieval Surgery (1 day): Transvaginal ultrasound-guided follicle aspiration, surgery time about 15-30 minutes, under intravenous or local anesthesia.
4. Fertilization and Embryo Culture (5-6 days): After egg and sperm combine, embryos are cultured to the blastocyst stage. PGT typically requires embryos to reach the blastocyst stage on day 5 or 6 for biopsy.
5. Embryo Biopsy and Freezing (1 day): An opening is made in the zona pellucida, and 5-10 trophectoderm cells are aspirated for testing. The biopsied blastocyst is immediately cryopreserved by vitrification.
6. Genetic Testing and Analysis (10-14 days): Whole genome amplification and sequencing/microarray analysis are performed on the biopsied cells. PGT-M requires additional time for linkage analysis verification.
7. Frozen Embryo Transfer (1 day): An embryo with normal chromosomes or without the pathogenic gene is selected and transferred after preparing the endometrium in a natural or artificial cycle.
8. Post-Transfer Support and Follow-up: Luteal phase support medication for 12-14 days, blood test for HCG to confirm pregnancy. Prenatal diagnosis (amniocentesis) is recommended after pregnancy to verify PGT results.

4. Suitable and Unsuitable Candidates for PGT

Suitable Candidates

• Female age ≥ 38 years, with previous miscarriage tissue confirmed as chromosomally abnormal.
• One or both partners are carriers of balanced translocation/Robertsonian translocation.
• Both partners are carriers of the same autosomal recessive genetic disease (e.g., thalassemia, spinal muscular atrophy).
• One partner is a patient or carrier of an autosomal dominant genetic disease (e.g., polycystic kidney disease, Marfan syndrome).
• Carriers of X-linked genetic diseases (e.g., hemophilia, Duchenne muscular dystrophy).
• History of ≥ 2 failed IVF cycles, where embryo chromosomal factors are considered highly likely.
• Recurrent miscarriage (≥ 2 spontaneous miscarriages), with miscarriage product testing indicating chromosomal abnormalities.

Unsuitable Candidates

• No clear genetic indication, only for "improving success rate" or "sex selection" purposes.
• Severely diminished ovarian reserve (AMH < 0.5 ng/mL, antral follicle count < 4), making it difficult to obtain enough eggs to form blastocysts.
• Poor embryo quality, unable to form blastocysts suitable for biopsy.
• The causative gene for the genetic disease is unclear, or an effective testing plan cannot be designed.
• Both partners cannot accept the risks of embryo biopsy and freezing.
• Uncontrolled systemic disease or reproductive tract infection, making an IVF cycle unsuitable.

5. PGT Considerations for Women of Different Ages

Age is the most critical factor affecting the normal chromosome rate in eggs and embryos. The value of PGT varies significantly among women of different ages.

It should be noted that PGT-A can only screen for embryos with normal chromosome numbers, but it cannot "improve" egg quality. For older women, the role of PGT-A is to help identify the chromosomally normal embryo among the limited ones available, thereby increasing the success rate per transfer, but it cannot increase the total number of embryos.

6. Most Easily Overlooked Details and Common Misconceptions

Most Easily Overlooked Details

• Limitations of PGT Testing: PGT-A can only detect numerical and large structural chromosomal abnormalities. It cannot detect microdeletions/duplications, single gene mutations (unless PGT-M is also performed), or imprinting gene abnormalities.
• Mosaicism Issue: About 5-10% of embryos are mosaic, containing both chromosomally normal and abnormal cells. The decision to transfer such embryos requires joint evaluation by a genetic counselor and clinician.
• Prenatal Diagnosis After PGT is Mandatory: PGT is a screening technology, not a diagnostic one. Amniocentesis or chorionic villus sampling is recommended after pregnancy to confirm the fetal chromosome and gene status.
• Transfer of Mosaic Embryos: Some reproductive centers allow the transfer of embryos with low-level mosaicism (< 40%), but this requires full informed consent and prenatal diagnosis during pregnancy.

Common Pitfalls

• Mistakenly believing PGT guarantees success: PGT can only screen for chromosomal/genetic issues; it cannot solve problems related to endometrial receptivity, immune factors, or endocrine abnormalities.
• Ignoring the male factor: Male age over 40 and increased sperm DNA fragmentation also raise the risk of embryo chromosomal abnormalities, but PGT-A has limited ability to detect sperm-derived chromosomal abnormalities.
• Over-pursuing blastocyst numbers: Some patients undergo repeated ovarian stimulation cycles just to accumulate enough blastocysts, ignoring the physical burden and time cost of each cycle. Clinical recommendation: if no normal embryos are obtained after 2-3 stimulation cycles, the plan should be reassessed.

7. Differences in PGT Policies Across Countries/Regions

The application of PGT technology varies significantly in regulations worldwide, directly affecting patient choice pathways.

Mainland China's regulatory system for PGT is moderately strict globally, emphasizing "medical necessity." This means that if a patient has no clear genetic indication, PGT cannot be performed in reproductive centers in Mainland China. Some patients therefore choose to go to countries or regions with more relaxed policies, but they must bear higher costs and the complexity of cross-border medical care.

8. Practitioner's Observation: Where is the Real Value of PGT?

Having worked in the field of assisted reproduction for over a decade, I have seen many patients with overly high expectations for PGT, and others who miss opportunities due to a lack of understanding. From the data, the value of PGT-A is clear in older women and those with recurrent miscarriage—it can increase the live birth rate per transfer from 20-30% to 40-50% and significantly reduce the miscarriage rate. But the prerequisite is that patients can obtain a sufficient number of blastocysts for screening.

The value of PGT-M for carriers of monogenic diseases is revolutionary. Take thalassemia as an example: for a couple where both partners are carriers of the same type of thalassemia, the probability of having a naturally conceived child with severe thalassemia is 25%. Through PGT-M, embryos not carrying the pathogenic gene can be selected for transfer, fundamentally preventing the birth of children with severe thalassemia. The significance of such applications goes far beyond "improving success rates."

At the same time, I have observed a tendency in some reproductive centers to overuse PGT. For patients under 35 with no genetic risk and undergoing their first IVF cycle, routinely recommending PGT-A is unnecessary. This not only increases the financial burden but also introduces biopsy risks. Before choosing PGT, be sure to thoroughly discuss the benefits and risks with a genetic counselor and clinician.

References: Technical Specifications for Preimplantation Genetic Testing from the Reproductive Medicine Branch of the Chinese Medical Association, ESHRE PGT Guidelines, and comprehensive clinical data from multiple domestic reproductive centers.