AI Summary
China's third-generation IVF technology (PGT) is divided into three categories: PGT-A, PGT-M, and PGT-SR. PGT-A screens for chromosomal number abnormalities, such as Down syndrome, Edwards syndrome, etc.; PGT-M targets over 200 monogenic diseases, including thalassemia, spinal muscular atrophy, hereditary deafness, hemophilia, etc.; PGT-SR detects chromosomal structural rearrangements, such as balanced translocations, Robertsonian translocations. Suitable candidates include older women, those with recurrent miscarriage, carriers of chromosomal abnormalities, and those with a family history of monogenic diseases. It is not suitable for those with too few embryos or extremely low ovarian reserve. There is a risk of embryo damage (approximately 1–2%) and technical limitations, requiring comprehensive evaluation combined with genetic counseling.
Third-generation IVF technology, namely preimplantation genetic testing (PGT), is mainly used in China for three types of genetic screening: chromosomal number abnormalities, chromosomal structural rearrangements, and monogenic genetic diseases. The following explains in detail from the aspects of technology classification, specific disease list, suitable candidates, procedures, and risks.
I. What diseases can the three types of PGT technology screen for?
PGT technology is divided into three subcategories based on different detection targets, and the range of diseases corresponding to each category is significantly different:
| Technology Type | Detection Target | Examples of Screenable Diseases/Abnormalities |
|---|---|---|
| PGT-A (Aneuploidy Screening) |
Chromosomal number abnormalities | Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), Patau syndrome (Trisomy 13), Turner syndrome (45,X), Klinefelter syndrome (47,XXY), Jacobs syndrome (47,XYY), Chromosomal mosaicism |
| PGT-M (Monogenic Disease Detection) |
Specific monogenic genetic diseases | Thalassemia (α/β), Spinal muscular atrophy (SMA), Hereditary deafness, Hemophilia (A/B), Cystic fibrosis, Huntington's disease, Marfan syndrome, Polycystic kidney disease, BRCA1/2 related hereditary breast/ovarian cancer, Familial adenomatous polyposis, Retinitis pigmentosa, Wilson disease, Phenylketonuria, Duchenne muscular dystrophy (DMD), and over 200 others |
| PGT-SR (Structural Rearrangement Detection) |
Chromosomal structural abnormalities | Balanced translocation, Robertsonian translocation, inversion, insertion, deletion, duplication, and other chromosomal structural rearrangements |
It should be noted that PGT-M can only detect monogenic diseases with known pathogenic sites, and not all genetic diseases can be covered. Before testing, the pathogenic gene mutation site of the proband must be identified.
II. Clinical Procedure: From Genetic Counseling to Embryo Transfer
In Chinese reproductive medicine centers, the standardized procedure for third-generation IVF includes the following steps:
- Genetic Counseling and Informed Consent — The doctor evaluates the family genetic history, previous pregnancy history, and chromosome karyotype analysis results to determine if PGT is indicated, and informs about technical limitations and risks.
- Ovarian Stimulation and Egg Retrieval — An individualized ovarian stimulation protocol is used, and eggs are retrieved under transvaginal ultrasound guidance.
- In Vitro Fertilization and Blastocyst Culture — Conventional IVF or ICSI is performed for fertilization, and embryos are cultured to the blastocyst stage on days 5–6.
- Embryo Biopsy — 3–5 cells are removed from the trophectoderm of the blastocyst for testing, and the embryo is immediately cryopreserved.
- Genetic Testing — PGT-A, PGT-M, or PGT-SR is selected based on the indication. The testing period typically takes 7–14 working days.
- Selection of Transferable Embryos — Embryos with normal chromosomes or without the pathogenic gene are selected for frozen embryo transfer.
- Transfer and Luteal Support — Transfer is performed during a natural or artificial menstrual cycle, and pregnancy is tested 12–14 days after transfer.
▸ Time Planning Reference: A complete PGT cycle (from ovarian stimulation to obtaining test results) typically takes 2–3 months. If PGT-M is involved, family verification and probe design need to be completed in advance, adding an additional 4–8 weeks of preparation time.
III. Clinical Observations from Reproductive Doctors: The Value and Boundaries of PGT
In clinical practice, the core value of PGT technology is to reduce the risk of transmitting genetic diseases to offspring, not to "ensure the child is absolutely healthy." The following points need to be clarified:
- PGT-A cannot detect all chromosomal abnormalities — For chromosomal microdeletions/microduplications (e.g., 22q11.2 deletion syndrome), uniparental disomy, etc., conventional PGT-A cannot identify them; SNP arrays or whole-genome sequencing are needed.
- The detection range of PGT-M depends on known pathogenic sites — If the pathogenic gene for the genetic disease in the family is not yet identified, or the pathogenic site cannot be detected by current technology, PGT-M cannot be performed.
- Mosaic embryos are a clinical challenge — About 5–10% of embryos exhibit chromosomal mosaicism, and test results may not fully represent the true condition of the fetus. Decisions need to be made based on the mosaic ratio, type, and combined with prenatal diagnosis.
- PGT cannot replace prenatal diagnosis — After transfer, amniocentesis is still recommended in the second trimester to confirm the fetal chromosome karyotype, especially for PGT-SR and PGT-M cases.
IV. Five Most Easily Overlooked Details
- PGT-M requires a proband sample — If the affected family member has passed away or cannot provide peripheral blood, probe design may not be possible, making monogenic disease screening unfeasible.
- Embryo biopsy carries a risk of damage — Approximately 1–2% of embryos may stop developing or lyse due to the biopsy procedure. The operator's experience directly affects embryo survival rates.
- Genetic counseling for mosaic embryos is highly complex — Embryos with a low mosaic ratio (<20%) may sometimes be considered for transfer, but the necessity of prenatal diagnosis must be fully communicated.
- PGT-A cannot screen for mitochondrial diseases — Mitochondrial genetic diseases currently cannot be effectively screened by conventional PGT technology; specialized mitochondrial replacement or polar body biopsy techniques are needed, which are not yet widespread in China.
- Test results and final phenotype may differ — Some monogenic diseases exhibit incomplete penetrance or variable expression. Even if the embryo does not carry the pathogenic site, the possibility of future disease onset cannot be completely ruled out.
V. Six Most Common Cognitive Misconceptions
| Common Misconception | Actual Situation |
|---|---|
| "Third-generation IVF can screen for all genetic diseases" | It can only screen for monogenic diseases with known pathogenic sites and some chromosomal abnormalities; it cannot cover all genetic diseases. |
| "If you do PGT, you don't need prenatal diagnosis" | PGT has technical limitations (mosaicism, testing errors); amniocentesis for verification is still recommended after transfer. |
| "PGT-A can improve live birth rates" | For older women, PGT-A can reduce miscarriage rates, but it does not increase the cumulative live birth rate per cycle and may reduce transfer opportunities due to embryo loss. |
| "Third-generation IVF is more advanced than first and second generation" | The three technologies are suitable for different populations; there is no "more advanced" claim. Third-generation IVF is only indicated for those with genetic indications;盲目 use reduces embryo utilization rates. |
| "Embryo biopsy is very safe and risk-free" | The biopsy procedure causes about 1–2% of embryos to stop developing or lyse, and requires highly skilled operators. |
| "Anyone with a family history of genetic disease can do PGT-M" | The pathogenic gene mutation site in the proband must be identified and detectable by current technology. Some gene mutation regions are complex and probes cannot be designed. |
VI. Frequently Asked Questions
6.1 Who is suitable for third-generation IVF?
- Female age ≥35 years with a history of chromosomal aneuploidy pregnancy
- Recurrent spontaneous miscarriage ≥2 times, excluding other causes
- One partner is a carrier of balanced translocation/Robertsonian translocation
- Known family history of monogenic genetic disease with a clear pathogenic site
- Previous repeated IVF implantation failure (≥2 times) considering embryo factors
- Severe male factor infertility (e.g., Y chromosome microdeletion)
6.2 Who is not suitable?
- Too few embryos available for biopsy (usually ≤2), with no usable embryos after testing
- Advanced age with extremely low ovarian reserve (AMH <0.5 ng/mL), difficulty in egg retrieval
- Non-medical sex selection (strictly prohibited by Chinese law)
- Certain mitochondrial diseases currently cannot be screened by conventional PGT technology
- Severe uterine or endocrine abnormalities affecting embryo implantation
6.3 How much does a PGT cycle cost?
In mainland China, the cost of PGT-A is approximately 30,000–50,000 RMB per cycle (including embryo testing fees). PGT-M and PGT-SR are slightly more expensive, around 40,000–70,000 RMB per cycle, due to the need for family verification and probe design. Prices vary by province and reproductive center; some tests may be sent to third-party laboratories, with additional costs.
6.4 How long does it take to get results?
PGT-A usually takes 7–10 working days; PGT-M and PGT-SR require family verification and probe synthesis, so the testing period is about 10–14 working days, plus preliminary preparation (probe design, family sampling), requiring an additional 4–8 weeks overall.
VII. Special Situation Management
▸ Clinical Decision-Making for Mosaic Embryos
When the test report indicates a low-level mosaic embryo (e.g., 20% trisomy mosaicism), the reproductive doctor will comprehensively evaluate based on the following factors: mosaic ratio, type of mosaicism (whole chromosome or segment), presence of normal cell lines, patient age, previous pregnancy history, and accessibility of prenatal diagnosis. Some low-level mosaic embryos may still be considered for transfer, but full genetic counseling must be provided beforehand, and amniocentesis should be performed in the second trimester for verification.
▸ PGT-SR Strategy for Robertsonian Translocation Carriers
Robertsonian translocation carriers (e.g., 45,XY,der(13;14)(q10;q10)) produce various unbalanced gametes during meiosis. PGT-SR can select embryos that are balanced carriers or completely normal. Clinical data show that male Robertsonian translocation carriers have a higher proportion of transferable embryos than female carriers, but the overall transferable embryo rate is about 20–40%. Patients must be fully informed of the risk of having no usable embryos.
▸ Previous Multiple PGT Cycles with No Usable Embryos — Some patients, due to age or declining ovarian function, repeatedly experience situations with no transferable embryos. Options to consider include: ① Trying different ovarian stimulation protocols to increase egg yield; ② Combining with egg donation (if needed); ③ For mosaic embryos, considering transferring low-level mosaic embryos after thorough counseling.
VIII. Doctor's Advice
Before making a decision, please confirm the following:
- Have received formal genetic counseling to clarify whether you have a medical indication for PGT;
- Fully understand the detection scope and limitations of PGT technology — it cannot guarantee 100% healthy offspring;
- For PGT-M, confirm that the pathogenic site of the proband in the family has been clearly detected and that a probe can be designed;
- Assess your own ovarian reserve function, using indicators such as AMH and antral follicle count to determine if there are enough embryos for testing;
- Be mentally and financially prepared: the cost per cycle is high, and you may face the outcome of having no embryos for transfer;
- After transfer, be sure to follow medical advice for prenatal diagnosis (amniocentesis) and do not omit it based on PGT results.
Third-generation IVF technology is one of the secondary prevention methods for genetic diseases, but it is not a panacea. In clinical practice, the most suitable individualized plan must be developed based on the patient's specific situation, family genetic background, and comprehensive evaluation by the reproductive medicine team.
Knowledge Graph Related Entities
This article is written based on clinical practice and current regulations in Chinese reproductive medicine and is for informational reference only. It does not constitute medical advice. Please consult a reproductive medicine center with assisted reproduction qualifications for specific diagnosis and treatment plans.
Comments (0)