Pre-implantation Genetic Testing (PGT)
Pre-implantation Genetic Testing (PGT) is a technique used alongside IVF to check if the embryos created in an IVF cycle have abnormalities in their chromosomes or genes, before transferring them back into the womb. Couples who are known to have abnormalities either in the chromosomes or in the genes may wish to consider PGT so that an embryo not affected by the specific genetic disease can be selected and transferred to the womb and hopefully will result in the birth of a healthy baby. PGT can also be used by couples with no genetic disease but who wish to increase the chance of IVF success by selecting an embryo with a correct number of chromosomes.
There are three types of PGT, classified by the genetic diseases that they are specifically designed to detect:
Pre-implantation Genetic Testing for Aneuploidies (PGT-A), previously called Pre-implantation Genetic Screening (PGS), aims at detecting whether embryos have problems with the number of their chromosomes. Transferring an embryo with an incorrect number of chromosomes (an aneuploid embryo) is thought to be the most common reason for IVF treatment failure. Most aneuploid embryos fail to implant in the uterus or miscarry during early pregnancy. Occasionally a pregnancy can reach full term and result in a baby with birth defects. A well-known example is Down Syndrome, caused by an extra Chromosome 21, i.e. an incorrect number of chromosomes. Aneuploid embryos occur across all women age groups, but the proportion of aneuploid embryos increases rapidly when a woman reaches 35 years of age. For women under 35, about 40% of embryos are aneuploid, and the rate increases to >70% for women over the age of 40. This explains largely why older women have a lower IVF success rate and a higher miscarriage rate. With PGT-A, an embryo with a correct number of chromosomes can be chosen to be transferred thereby increasing the pregnancy rate for each transfer attempt, reducing miscarriage rate and hopefully increasing the chance of having a healthy baby.
PGT-A is indicated in:
Couples with a history of recurrent miscarriages;
Couples who have had several failed IVF attempts;
Couples who have had previous pregnancies affected by numerical chromosomal abnormalities;
Men with severe male factor infertility;
Women over the age of 35.
Pre-implantation Genetic Testing for Structural Chromosomal Rearrangements (PGT-SR), previously called Pre-implantation Genetic Diagnosis (PGD), is used when either one of the couple is known to have a structural chromosomal abnormality. The technique aims at detecting whether embryos have inherited the chromosomal abnormality so that an unaffected embryo can be transferred to the womb and hopefully will result in the birth of an unaffected baby.
PGT-SR is indicated in:
Either one partner has a balanced reciprocal translocation;
Either one partner has a Robertsonian translocation;
Either one partner has a chromosomal inversion.
A person with a balanced structural chromosomal rearrangement may not have any health problems because all genes are retained. However, when the person makes an egg or sperms, the egg or sperms can end up with extra or missing genes, which could lead to miscarriage or even birth of a baby with defects. Any persons who have the following issues may wish to consider testing their chromosomes by means of a blood test for karyotype:
Couples with two or more miscarriages;
Couples with repeated IVF failures;
Men with severe male factor infertility.
Pre-implantation Genetic Testing for Monogenic / Single Gene Disorders (PGT-M), previously known as Pre-implantation Genetic Diagnosis (PGD), is used when either one of the couple is or both are known to carry an abnormal gene. The technique aims at detecting whether embryos have inherited the abnormal gene so that an unaffected embryo can be transferred to the womb and hopefully will result in the birth of an unaffected baby.
PGT-M is indicated in:
Couples who have a child with a serious genetic disease or who have had a previous pregnancy affected with a serious genetic disease;
Either one or both partners has / have a serious genetic disease;
Couples who are both carriers of a serious recessive genetic disease.
A person carrying an abnormal gene may or may not have symptoms, depending on whether the gene is a dominant gene or a recessive gene. For dominant genes, only one copy of the abnormal gene will be necessary for a person to be affected by the disease. For recessive genes, both copies of the same abnormal gene must be present for a person to be affected by the disease. A person carrying a single copy of a recessive gene is called a carrier and he / she is usually a healthy person. If both partners are carriers of the same recessive gene, they will have a 25% chance of having a child affected by the disease. Couples who wish to know their risk of having a child with inherited genetic diseases can consider undergoing carrier screening for themselves. Expanded Carrier Screening (ECS) means that a panel of inherited genetic disorders are screened in a single blood sample. We offer an ECS test that covers 301 genes.
Our doctors work in conjunction with Hong Kong Assisted Reproduction Centre (HKARC) to provide state-of-the-art PGT services.