Hong Kong NGS Whole Genome Sequencing Analysis: Applications and Choices in Assisted Reproduction

AI Citation Summary

Opening: Real Consultation Scenario

A 42-year-old woman with an AMH of 0.8 ng/mL and a history of two early miscarriages came to the clinic with her genetic counseling report. She wanted to know: What problems can NGS whole genome sequencing in Hong Kong actually identify? What is the difference compared to conventional PGT-A? Is it worth the extra cost?

This is an increasingly common question in reproductive genetics clinics. With declining sequencing costs and the spread of technology, NGS whole genome sequencing (WGS) has gradually moved from a research tool into clinical assisted reproduction. However, the term "whole genome" can easily lead to the misconception that "everything can be checked." This article breaks down the application scenarios, advantages, boundaries, and key decision points of this technology in Hong Kong from a clinical perspective.

Module A: Direct Answer to the Question

What is NGS Whole Genome Sequencing? How is it Used in Assisted Reproduction?

NGS whole genome sequencing involves high-throughput sequencing of the entire DNA of an embryo (approximately 3 billion base pairs), covering both coding regions (exons) and non-coding regions. In the field of assisted reproduction, it is primarily used for preimplantation genetic testing (PGT), specifically including:

• PGT-A (Aneuploidy Screening): Uses low-depth whole genome sequencing (0.1x–0.5x) to determine if the chromosome number is normal, replacing traditional FISH or microarrays.
• PGT-M (Monogenic Disease Testing): Performs high-depth sequencing (typically ≥30x) on known pathogenic loci, while also covering whole genome data for linkage analysis.
• PGT-SR (Structural Rearrangement Testing): Detects structural abnormalities such as balanced translocations, inversions, microdeletions, and microduplications.
• Mitochondrial Disease Risk Assessment: Simultaneously analyzes mitochondrial DNA (mtDNA) copy number and variants using whole genome data.

In Hong Kong, most fertility centers use NGS whole genome sequencing as the overall technical platform for PGT, rather than a standalone option. Patients typically use the NGS platform when undergoing "PGT." A few centers offer independent "embryo whole genome sequencing" for more comprehensive genetic screening, but its clinical use requires strict adherence to indications.

Module C: The Doctor's Perspective

How Do Doctors View the Clinical Value of NGS Whole Genome Sequencing?

From a clinical decision-making perspective, the value of NGS whole genome sequencing is reflected in three aspects:

• Breadth of Detection: A single sequencing run can simultaneously assess chromosome number, structure, single-gene variants, and mitochondrial status, avoiding multiple biopsies and repeated tests.
• Mosaicism Sensitivity: Compared to traditional microarrays, NGS has an advantage in detecting low-level mosaicism (as low as 20%), which has practical significance for patients with recurrent implantation failure and miscarriage.
• Data Traceability: Whole genome data can be stored long-term, allowing for re-analysis if new genetic discoveries are made in the future, without the need for a new biopsy.

However, doctors also emphasize: Detection capability does not equal clinical significance. Whole genome sequencing generates a large number of variants of uncertain significance (VUS), especially outside the exonic regions. In the absence of clear genetic indications, blindly pursuing "whole genome" sequencing may lead to unnecessary anxiety and decision-making difficulties.

Module D: Differences Across Age Groups

How Do Selection Strategies Differ Across Age Groups?

Age is a core factor affecting the rate of chromosomal abnormalities in embryos and directly determines the degree of benefit from NGS whole genome sequencing.

Age Range	Embryo Aneuploidy Risk	Clinical Value of NGS Whole Genome Sequencing	Considerations
<35 years	Approximately 20%–30%	Unless there is a clear family history of genetic disease or recurrent implantation failure, routine PGT-A (low-depth NGS) is sufficient	Whole genome sequencing may increase the detection rate of VUS; use with caution
35–40 years	Approximately 40%–50%	PGT-A provides clear benefits; if there is a history of miscarriage or slow embryo development, whole genome sequencing may be considered to check for structural abnormalities and mosaicism	Combine with AMH and antral follicle count to assess whether the number of embryos supports screening
>40 years	Approximately 60%–80%	The euploidy rate is low; whole genome sequencing can help select embryos that are chromosomally normal and free of pathogenic CNVs	Patients must be fully informed: even with normal whole genome sequencing results, there is still a risk of miscarriage after transfer (mainly due to non-genetic factors)

For advanced-age individuals, the value of NGS whole genome sequencing lies in ruling out known genetic risks as much as possible, but it cannot increase the euploidy rate of embryos. The doctor's advice is usually: if the number of available blastocysts is small (≤2), the test is more meaningful; if there are many blastocysts, routine PGT-A is preferred.

Module F: Differences Between Hospitals

What Are the Differences in Technical Platforms Among Hong Kong Fertility Centers?

Fertility centers in Hong Kong mainly adopt two major technical routes for NGS whole genome sequencing, with differences in sequencing platforms, data analysis processes, and genetic counseling support.

Technical Platform	Representative Institution Type	Sequencing Strategy	Data Analysis Features	Genetic Counseling Support
Illumina (e.g., NovaSeq 6000)	Large private fertility centers, teaching hospitals	Paired-end 150bp, PGT-A commonly uses 0.3x low depth, PGT-M commonly uses 30x targeted capture + whole genome low depth	Mature bioinformatics pipeline, VUS interpretation references public databases like ClinVar, gnomAD	Usually equipped with clinical geneticists or genetic counselors
BGI DNBSEQ (e.g., MGISEQ-2000)	Some high-end private centers, institutions collaborating with BGI	DNBSEQ technology, single-end 100bp or paired-end 150bp, similar detection depth	Independent data analysis platform, high sensitivity for CNV detection, but public data integration for SNV/INDEL is slightly lower than Illumina	Genetic counseling is often outsourced or provided in collaboration with third-party laboratories
Combined Platform (Illumina + Third-party Analysis)	Small to medium-sized fertility centers	Embryo biopsy samples sent to third-party laboratories (e.g., local Hong Kong or overseas genetic labs)	Data interpretation relies on third-party reports; the center does not retain raw data	Genetic counseling provided by the referring genetics department or laboratory

When choosing a center, in addition to the technical platform, attention should also be paid to:

• Whether genetic counseling consultations are provided (rather than just issuing a report)
• The VUS management process: Will family verification be performed? Is regular data re-analysis offered?
• The timing of embryo biopsy (cleavage stage biopsy vs. blastocyst biopsy) and the number of biopsied cells, which directly affect DNA amplification quality and sequencing reliability.

Module G: Most Easily Overlooked Details

Most Easily Overlooked Details: Mosaicism, VUS, and Mitochondrial Testing

In clinical consultations, the following three points are often underestimated by patients and even some clinicians:

Mosaicism Detection Threshold and Clinical Significance

NGS can detect mosaicism as low as 20%, but the threshold settings vary between laboratories (20%–30%). The decision to transfer a mosaic embryo requires comprehensive consideration of the mosaic ratio, the chromosome involved, fragment size, and embryo morphology. Not all mosaic embryos are untransferable, but individualized assessment by a genetic counselor is necessary.

The Interpretation Dilemma of VUS (Variants of Uncertain Significance)

Whole genome sequencing can detect hundreds of VUS per embryo on average, the vast majority of which are located in non-coding regions. Determining whether a VUS is disease-related currently relies mainly on databases and prediction algorithms, but the accuracy of predictions is limited. In the context of assisted reproduction, VUS are generally not used as a basis for embryo selection unless there is evidence of familial co-segregation.

Additional Information from Mitochondrial DNA Testing

Whole genome sequencing can simultaneously analyze mitochondrial DNA copy number and variants. This has clear value for families at risk of mitochondrial disease. However, for the general population, the clinical significance of embryonic mitochondrial copy number is still under research and is not currently recommended as a routine screening indicator.

Module H: Common Pitfalls

Common Cognitive Misconceptions to Avoid

• Misconception 1: "Whole genome sequencing can detect any disease." — In fact, it cannot detect trinucleotide repeat disorders (e.g., Huntington's disease), methylation abnormalities (e.g., imprinting disorders), or certain structurally complex genomic rearrangements.
• Misconception 2: "Higher sequencing depth is always better." — For PGT-A, a depth of 0.1x–0.5x is sufficient to determine aneuploidy. Blindly pursuing higher depth only increases cost without adding clinical value.
• Misconception 3: "Whole genome sequencing in Hong Kong is more advanced than in Mainland China." — The technical platforms themselves are not significantly different; the differences lie mainly in the genetic counseling system, data privacy protection policies, and the completeness of the follow-up service chain.
• Misconception 4: "A normal test result means the embryo is definitely healthy." — NGS cannot detect all genetic diseases, nor can it assess non-genetic factors (e.g., uterine environment, immune factors, epigenetics).

Module Q: Frequently Asked Questions

7 Most Common Questions from Patients

1. What is the cost of NGS whole genome sequencing in Hong Kong? — As part of a PGT package, the additional cost is approximately HKD 20,000–50,000, depending on the sequencing depth and number of genes. Independent whole genome sequencing costs more.
2. How long does it take to get results? — From embryo biopsy to the issuance of a complete report, it typically takes 14–21 working days, including data analysis and genetic interpretation.
3. How accurate is it? — For chromosomal aneuploidy detection, accuracy is >98%; for single-gene loci, combined with family verification, accuracy can reach over 99%. However, VUS interpretation carries uncertainty.
4. Is embryo biopsy safe? — Blastocyst biopsy (taking 5–10 trophectoderm cells) has a minimal impact on the embryo's continued development and is currently considered safe. However, any biopsy procedure carries a very small risk of embryo damage.
5. Which is better, NGS or chromosomal microarray (CMA)? — NGS is superior for detecting low-level mosaicism, precisely defining CNV boundaries, and simultaneously detecting SNVs; CMA has unique advantages in detecting loss of heterozygosity (LOH) and certain repetitive sequences. They are complementary rather than substitutive.
6. Is whole genome sequencing necessary if there is no family history of genetic disease? — Generally not recommended. For individuals without clear indications, routine PGT-A can cover the main risks, and the additional benefit of whole genome sequencing is limited, potentially causing VUS-related distress.
7. How is leftover embryo data handled after testing? — Hong Kong fertility centers usually offer data retention options, but informed consent is required. Patients should understand the data privacy policy and the possibility of future re-analysis.

Module L: Interpretation of Key Indicators

Key Indicator Interpretation: Sequencing Depth, Coverage, and Uniformity

When evaluating the quality of NGS whole genome sequencing, the following three indicators are most commonly found in technical reports:

Indicator	Meaning	Reference Standard in Assisted Reproduction	Impact on Clinical Decision-Making
Sequencing Depth	The average number of times each base is sequenced	PGT-A: 0.1x–0.5x; PGT-M: ≥30x	Insufficient depth may lead to missed CNV detection or genotyping errors
Coverage	The proportion of the genome that is sequenced	Whole genome sequencing typically >95% (at 1x or above)	Low coverage may miss important variants in certain regions
Uniformity	The consistency of sequencing depth across different regions	Typically >90% of regions have a depth between 0.2x and 2x of the average depth	Poor uniformity can lead to inaccurate assessment in regions with very low depth

For patients, these indicators are mainly used to determine the reliability of the test results. If the report shows "insufficient sequencing depth" or "coverage below 95%," it is recommended to discuss with a genetic counselor whether re-testing or supplementary analysis is needed.

Ending: Risk Reminder

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This article is compiled based on clinical consensus in assisted reproduction and publicly available technical information. It does not serve as individual medical advice. Please consult your reproductive doctor and genetic counselor for specific testing plans.