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Pre-implantation Genetic Testing
One-stop flexible PGT-Plus
The Chinese University of Hong Kong set up the territory’s first outpatient genetic clinic to provide one-stop diagnosis and consultation services. The clinic is now conducted in Prince of Wales Hospital including genetic counseling, risk assessment and genetic and genomic testing. The scope of services includes congenital malformation, growth disorders, metabolic disease, cancer, recurrent abortion and any diseases associated with genetic defects, such as autism and developmental delay.
Genetic Testing
Preimplantation Genetic Testing for Aneuploidies (PGT-A)
- Gains or losses of chromosomes (aneuploidy) and large chromosome segments of ≥4 million base pairs (Mb) in size
- ≥30% chromosomal mosaicism
- Triploidy & Uniparental isodisomy (isoUPD)
Preimplantation Genetic Testing for Monogenic Disorders (PGT-M)
- Detection of targeted monogenic disorders
Preimplantation Genetic Testing for Structural Rearrangements (PGT-SR)
- Reduces the likelihood of transferring an embryo with unbalanced chromosomal rearrangement
- Balanced translocation carrier can be detected
The test is suitable for:
- Advanced maternal age (age 35 or above)
- Recurrent miscarriages
- Recurrent implantation failure
- Severe male factor infertility
- Carriers or affected individuals of monogenic disorders (PGT-M)
- Carriers of a balanced chromosome translocation (PGT-SR)
Sample requirement
How does PGT improve IVF success?
When an embryo carries an incorrect number of chromosomes, it often fails to implant or results in early miscarriage. Some chromosomally abnormal pregnancies can survive to term but may lead to abnormal live birth. For example, Down syndrome (Trisomy 21). Besides numerical abnormalities, other genetic alterations include polyploidy, genome-wide uniparental isodisomy can be associated with imprinting defects and molar pregnancies. PGT screens embryos to identify those that are likely to contain the correct number of chromosomes with normal biparental inheritance.
Advantages of PGT
- Improve implantation rate in those with recurrent implantation failure
- Reduce the subsequent miscarriage risk in couples with recurrent pregnancy loss
- Reduce risk of birth defects
- Reduce risk of multiple pregnancies by single embryo transfer (SET)
- Against known familial/targeted genetic mutations and structural rearrangements for intrauterine transfer
Limitations
PGT-A
It cannot detect sub-microscopic abnormalities less than 4 Mb. In addition, mosaicism may lead to the PGT-A result not being representative of the embryo.
PGT-M/-SR
Misdiagnosis due to amplification bias, allele drop-out, and recombination can never be ruled out. Prenatal diagnosis via amniocentesis is strongly recommended if clinical pregnancy is achieved.
