Chromosomal Abnormalities in China for PGT: Indications, Policies, and Procedure

Can Patients with Chromosomal Abnormalities Undergo PGT: Physician Decision-Making Logic

In reproductive genetics clinics, patients with chromosomal abnormalities who come for consultation generally fall into two categories: one group knows they have a balanced translocation, Robertsonian translocation, or inversion and seek treatment due to recurrent miscarriage or having had a child with abnormalities; the other group first discovers the chromosomal issue during infertility testing or analysis of miscarriage tissue. Faced with the question "Can I do PGT?", doctors typically do not answer with a simple "yes" or "no." Instead, they first review the karyotype report to distinguish the type of abnormality, then consider the couple's age, ovarian reserve, reproductive history, and the assisted reproductive technology approval policies of their province to comprehensively assess the medical necessity and feasibility of PGT.

The clinical term for PGT is preimplantation genetic testing, which includes PGT-A (aneuploidy screening), PGT-M (monogenic disease testing), and PGT-SR (structural rearrangement testing). Patients with chromosomal structural abnormalities primarily correspond to PGT-SR, while some carriers of chromosomal abnormalities who are of advanced maternal age or have diminished ovarian reserve may also require PGT-A simultaneously. Technically, reproductive centers in China with PGT qualifications can perform PGT-SR, but not all chromosomal abnormalities are suitable for PGT, and not everyone who meets the medical indications can directly enter a cycle—they must go through genetic counseling, approval from the hospital's ethics committee, and verification of embryo testing capabilities.

When is PGT Suitable: Indication Boundaries for Patients with Chromosomal Abnormalities

According to the "Technical Specifications for Preimplantation Genetic Testing" and the clinical practice of major domestic reproductive centers, chromosomal abnormalities suitable for PGT include:

• Reciprocal Translocations: Including balanced and complex translocations. Carriers have a higher proportion of unbalanced gametes after natural conception, significantly increasing miscarriage rates. PGT-SR can select embryos that are normal or balanced carriers.
• Robertsonian Translocations: Commonly occurring between chromosomes 13, 14, 15, 21, and 22. The theoretical probability of carriers having a chromosomally normal child is about 1/6 to 1/3. PGT-SR can reduce the risk of recurrent miscarriage or birth defects.
• Chromosomal Inversions: Especially pericentric inversions with large segments, where the risk of producing unbalanced gametes is increased, making PGT-SR suitable.
• Chromosomal Numerical Abnormalities: Such as Turner syndrome (45,X) mosaicism, Klinefelter syndrome (47,XXY) mosaicism, etc. Some patients can use PGT-A to screen for euploid embryos, but this requires a comprehensive assessment based on the specific mosaic ratio and reproductive risk.
• Previous Child with Chromosomal Abnormality: Even if both parents have normal peripheral blood karyotypes, if they have previously had a child with a chromosomal numerical or structural abnormality, the risk of recurrence is higher than the general population. PGT-A or PGT-SR may be considered.

Conditions that are unsuitable or require careful evaluation include:

• Chromosomal Polymorphisms: Such as increased heterochromatin regions on chromosomes 1, 9, or 16, or length variations in the long arm of the Y chromosome. These usually do not increase the risk of miscarriage or birth defects and generally do not require PGT.
• Low-Level Mosaicism: When the mosaic ratio in peripheral blood is below 10%, the proportion of abnormal chromosomes in gametes is usually even lower. The benefit of PGT is limited and requires individualized decision-making based on reproductive history.
• Severely Diminished Ovarian Reserve: Too few retrieved oocytes may not yield enough embryos for testing, leading to a high cycle cancellation rate. The expected number of testable embryos should be assessed in advance.
• Concurrent Uterine Structural Abnormalities or Recurrent Implantation Failure: Chromosomal abnormalities and endometrial receptivity issues are two independent factors. Non-genetic factors affecting implantation must be ruled out first; otherwise, even transferring normal embryos may still result in failure.

Why Chromosomal Abnormalities Increase Reproductive Risk: A Reproductive Medicine Perspective

Carriers of chromosomal structural abnormalities are usually phenotypically normal because the total amount of genetic material has not increased or decreased, only rearranged. However, during gamete formation, homologous chromosomes pair and exchange during meiosis. Translocated or inverted chromosomes cannot pair normally, easily leading to unbalanced gametes—where some gene segments are duplicated and others deleted. This imbalance can cause the embryo to stop developing in the early stages, manifesting as a biochemical pregnancy or early miscarriage. Some unbalanced embryos may continue to develop, but the child may be born with multiple malformations, intellectual disabilities, or developmental delays.

Taking a balanced translocation as an example, only about 1/4 to 1/9 of the gametes produced by a carrier are balanced (normal or carrier), with the rest being unbalanced. The exact ratio depends on the breakpoints of the translocated chromosomes, the length of the chromosomes involved, and the sex (male carriers typically produce a lower proportion of normal gametes than females). Therefore, patients with chromosomal abnormalities have significantly higher rates of miscarriage and abnormal pregnancies after natural conception compared to the general population. This is the most important value of PGT for this group—using embryo testing to select balanced or normal embryos for transfer, thereby reducing the risk of miscarriage and birth defects.

Differences in PGT Policies Across Countries: China, USA, Thailand, Japan

The conditions and restrictions for patients with chromosomal abnormalities undergoing PGT vary by country, mainly in approval processes, scope of indications, and ethical requirements:

For Chinese patients, if their specific chromosomal abnormality is not clearly supported by current domestic regulations, or if the local reproductive center cannot perform PGT-SR due to ethical approval limitations, some patients choose to go to countries with more flexible policies. However, they must also consider the legal risks of overseas medical treatment, difficulties in follow-up, and compliance requirements for embryo transport.

Easily Overlooked Details: Three Preparations Before PGT for Chromosomal Abnormalities

Before deciding to undergo PGT, three steps are often overlooked or underestimated by patients, directly affecting the smooth progress of the subsequent process:

• Simultaneous Karyotype Analysis of Both Partners: Some patients think it is enough to check only their own chromosomes. However, if the spouse also carries a chromosomal abnormality (e.g., both have balanced translocations or one has a Y-chromosome microdeletion), the genetic pattern and testing strategy will be completely different. High-resolution karyotyping for both partners is essential, and FISH or chromosomal microarray analysis may be needed.
• Genetic Counseling Report Must Include Reproductive Risk Assessment: Some hospitals only report the type of abnormality in the karyotype report without providing specific reproductive risk probabilities or the expected benefit of PGT-SR. It is recommended to seek re-evaluation at a reproductive center or genetics clinic with genetic counseling qualifications to obtain a formal genetic counseling record, which is a mandatory document for PGT ethics approval.
• Confirm the Reproductive Center Has PGT-SR Capability: Currently, the number of reproductive centers in China approved to perform PGT is limited, and some centers only have PGT-A qualifications, not PGT-SR. If planning to do PGT-SR, it is necessary to confirm in advance whether the center has the corresponding laboratory conditions and experience to avoid discovering later that testing cannot be completed.

Actual Process: Nine Steps from Genetic Counseling to Embryo Transfer

The standard process for patients with chromosomal abnormalities undergoing PGT at a formal reproductive center in China is roughly as follows:

1. Genetic Counseling Clinic: Bring both partners' karyotype reports, previous miscarriage tissue analysis reports (if any), and reproductive history. The genetic counselor assesses the indications and expected benefits of PGT.
2. Fertility Assessment: Female checks AMH, FSH, LH, antral follicle count; male checks semen analysis to determine if current fertility levels support entering a cycle.
3. Ethics Approval Application: Submit genetic counseling report, informed consent forms, ID cards of both partners, marriage certificate. Some centers may also require household registration or residence proof. Wait for ethics committee approval (usually 2-4 weeks).
4. File Creation and Cycle Start: After approval, complete file creation, pre-operative tests (infectious diseases, coagulation, liver and kidney function, etc.), and develop an individualized ovarian stimulation protocol.
5. Egg Retrieval and Sperm Collection: After ovarian stimulation, undergo egg retrieval surgery. Collect sperm on the same day for ICSI fertilization (PGT must use ICSI to avoid interference from additional genetic material carried by sperm).
6. Embryo Culture and Biopsy: Fertilized eggs are cultured to the blastocyst stage (day 5-6). An embryologist creates a hole in the zona pellucida and removes 3-5 trophectoderm cells for genetic testing.
7. Genetic Testing: Choose PGT-SR or PGT-A+SR based on the type of abnormality. The testing period usually takes 2-4 weeks.
8. Frozen Embryo Transfer: After results are available, select normal or balanced carrier embryos for frozen-thawed transfer.
9. Prenatal Diagnosis Confirmation: After successful transfer, amniocentesis for prenatal karyotype analysis is required during pregnancy to confirm that the fetal chromosome results are consistent with the embryo testing.

Timeline: How Long Does a PGT Cycle Take for Chromosomal Abnormalities?

From the first genetic counseling session to the final transfer, a complete PGT cycle for patients with chromosomal abnormalities typically takes 4-6 months, which is 1-2 months longer than a conventional IVF cycle. The specific time distribution is as follows:

• Genetic Counseling and Ethics Approval: 2-4 weeks (if documents are complete and the center's approval process is smooth)
• Pre-operative Tests and File Creation: 1-2 weeks (some tests can be started at any time during the menstrual cycle)
• Ovarian Stimulation and Egg Retrieval: 2-4 weeks (depends on ovarian response and protocol choice)
• Embryo Culture and Biopsy: 5-7 days (from egg retrieval to completion of blastocyst biopsy)
• Genetic Testing: 2-4 weeks (PGT-SR takes slightly longer than PGT-A because it requires custom probe design or whole genome amplification analysis)
• Frozen-Thawed Transfer: 4-6 weeks (requires endometrial preparation, either natural cycle or hormone replacement cycle)

If the first cycle yields insufficient oocytes or no transferable embryos, repeated cycles will extend the total time. It is recommended that patients with chromosomal abnormalities allow a time window of at least 6-8 months to avoid compromising decision quality due to time constraints.

Frequently Asked Questions: Five Most Common Questions from Patients with Chromosomal Abnormalities

Question 1: If a balanced translocation carrier undergoes PGT, is it guaranteed that a normal embryo will be found?
Not necessarily. Whether a normal or balanced embryo can be found depends on the type of translocation, the breakpoint location, and the number of blastocysts obtained. If more than 5 blastocysts are obtained, the probability is higher; if only 1-2 blastocysts are available, the chance of all being abnormal is not low. For some patients with complex translocations or breakpoints near the telomere, the proportion of normal embryos may be even lower.

Question 2: If a balanced carrier embryo is selected by PGT, will the child have the same fertility problems as me when they grow up?
Balanced carriers do face the same risk during reproduction—producing unbalanced gametes leading to miscarriage or abnormal pregnancy. However, this fertility issue is manageable through prenatal diagnosis and future reproductive technologies (including PGT-SR). Whether to transfer a balanced carrier embryo requires thorough discussion with a genetic counselor before transfer to make an informed choice.

Question 3: Is PGT mandatory for all chromosomal inversions?
Not all inversions require it. The genetic risk of an inversion mainly depends on the size and location of the inverted segment. For paracentric inversions with small segments that do not contain critical genes, the risk of producing unbalanced gametes is low. Natural conception with prenatal diagnosis can be attempted after genetic counseling. PGT-SR is only recommended for inversions with large segments or those involving important gene regions.

Question 4: Will the child be completely normal after PGT?
PGT can screen for specific chromosomal abnormalities but cannot detect all genetic diseases, single-gene mutations, or birth defects caused by non-genetic factors. Routine prenatal screening and diagnosis are still required after transfer, including NT scan, non-invasive DNA testing, and amniocentesis.

Question 5: Which reproductive centers in China can perform PGT-SR for chromosomal abnormalities?
As of 2025, there are about 80 reproductive centers in China with PGT qualifications, of which approximately 50-60 can perform PGT-SR. It is recommended to prioritize centers with over 200 testing cycles per year and independent genetics laboratories, as they have more extensive testing experience.

Special Situation Management: Strategies for Chromosomal Abnormalities Combined with Other Fertility Issues

In clinical practice, about 20% of patients with chromosomal abnormalities also have other factors affecting fertility, which need to be addressed in layers:

• Combined with Diminished Ovarian Reserve: If AMH is below 1.0 ng/mL or antral follicle count is less than 5, the number of oocytes retrieved in a direct PGT cycle may be insufficient. Consider attempting 1-2 egg retrievals to accumulate embryos, or add support like growth hormone or CoQ10 to the stimulation protocol. Perform biopsy and testing once enough embryos are obtained.
• Combined with Male Factor: If the male is a carrier of a chromosomal abnormality and also has severe oligoasthenospermia, first assess suitability for ICSI. Consider testicular sperm aspiration or donor sperm if necessary. If the male has a Y-chromosome microdeletion, identify the type—patients with AZFc deletion may still achieve offspring via ICSI, but complete AZFa or AZFb deletion offers no effective sperm retrieval option.
• Combined with Recurrent Implantation Failure: For patients with chromosomal abnormalities, recurrent implantation failure first requires ruling out causes other than embryonic chromosomal abnormalities, including endometrial receptivity, chronic endometritis, and immune factors. It is recommended to complete hysteroscopy + endometrial microbiome analysis + immunohistochemistry before starting a PGT cycle to avoid failure due to non-genetic factors even after PGT.

Practitioner Observations: Three Common Misconceptions in PGT Decision-Making for Chromosomal Abnormalities

In clinical work, it has been observed that patients with chromosomal abnormalities often fall into three cognitive biases when deciding about PGT:

The first misconception is thinking "PGT guarantees a healthy child." In reality, PGT can only screen for known chromosomal abnormalities and cannot cover all genetic diseases or developmental issues. Furthermore, embryo testing itself has technical limitations—about 1-2% of results may be false positive or false negative, so prenatal diagnosis is still needed after transfer.

The second misconception is "Chromosomal abnormalities are rare, and doctors may not be familiar with them." The carrier rate of balanced translocations in the general population is about 0.2%, but it can reach 5-10% in couples with recurrent miscarriage, so it is not rare. However, experience with PGT-SR varies significantly between reproductive centers. It is advisable to choose centers that perform over 50 PGT-SR cycles per year, as their embryology labs are more experienced in analyzing translocation breakpoints, probe design, and mosaic interpretation.

The third misconception is "If no normal embryo is found in the first cycle, there is no hope at all." Some patients may get all abnormal embryos in one cycle, but this could be due to a low oocyte yield or a suboptimal stimulation protocol. Changing the stimulation protocol for a second retrieval, or combining with a follicle-stimulating protocol, may still yield normal embryos. It is recommended to review the first cycle's embryo testing results with the doctor, analyze whether the abnormality type shows a pattern, and then decide on the next step.

Risk Reminder: Key Decision-Making Points Before PGT

Before undergoing PGT, patients with chromosomal abnormalities need to be aware of the following risks and be mentally prepared:

• Some chromosomal structural abnormalities (e.g., complex translocations, small inversions) may lead to PGT-SR test failure or inconclusive results. Check the center's testing success rate in advance.
• Even if a normal embryo is identified by PGT-SR, the implantation rate after transfer is about 40-50%, not 100%.
• The cost of PGT is higher than conventional IVF, adding an average of 30,000-50,000 RMB per cycle. There is also a risk of losing the entire testing fee if no results are obtained or no transferable embryo is found.
• Prenatal diagnosis to confirm fetal chromosomes is mandatory after pregnancy. Patients who do not accept prenatal diagnosis are not suitable for PGT.