What is Preimplantation Genetic Testing (PGT)?
Pre-implantation genetic testing is an assisted reproduction technique that allows the genetic makeup of the embryo to be analysed, thereby preventing the transfer of non-viable embryos or those with genetic disorders, and ensuring that only healthy embryos are transferred to the uterine cavity.
Preimplantation genetic testing involves performing an embryo biopsy: several cells are extracted from the trophectoderm — the part of the embryo that will develop into structures such as the placenta. These samples are then analysed in the genetics laboratory to identify embryos with abnormalities and select the healthy ones.
Types of Preimplantation Genetic Testing
PGT-A (Preimplantation Genetic Testing for Aneuploidy Screening) — this type of preimplantation genetic testing detects chromosomal abnormalities in embryos. For example, Down syndrome occurs when there are three copies of chromosome 21 (trisomy 21) instead of two. These alterations are primarily associated with **advanced maternal age**.
PGT-M (Preimplantation Genetic Testing for Monogenic Diseases) — this involves the genetic analysis of embryos whose parents are carriers of or affected by a genetic disease. PGT-M prevents the transmission of these conditions to the next generation.
Stages of Preimplantation Genetic Testing
Preimplantation genetic testing is a complementary technique within the IVF (In Vitro Fertilization) treatment process. The steps of a preimplantation genetic testing cycle are:
Egg fertilisation and embryo culture
- The first step is to perform IVF usually using the ICSI technique (intracytoplasmic sperm injection).
- The embryos obtained are placed in our Embryoscope (Time-Lapse) incubator and cultured until day 5–6, the blastocyst stage. At this point the embryo is made up of two cell groups: the trophectoderm (the future placenta) and the inner cell mass, which gives rise to the embryo itself. Love Fertility Clinic includes Embryoscope in every treatment that involves preimplantation genetic testing (PGT).
Embryo biopsy
The embryo biopsy is performed when the embryo reaches the blastocyst stage (day 5–6).
Years ago, the biopsy was carried out on day 3, when the embryo had around 8 cells. Today, advances in embryology training and laboratory technology allow us to culture embryos reliably to the blastocyst stage. Waiting until this point is highly recommended: it gives us greater insight into embryo viability and allows us to carry out the procedure with more confidence and safety for the embryos.
The technique uses a laser to create a small opening in the zona pellucida, and several cells are extracted from the part of the embryo that will form the placenta.
Genetic analysis
The sample obtained from the biopsy is placed in a special tube for subsequent analysis in the genetics laboratory, using molecular biology techniques such as FISH, NGS, and PCR, among others.
The embryos remain cryopreserved at Love Fertility until the results are available. Euploid embryos (chromosomally healthy) are kept vitrified until transfer to the patient’s uterus; aneuploid embryos (chromosomally abnormal) are discarded.
When is preimplantation genetic testing recommended?
Preimplantation genetic testing is recommended in the following cases:
- To optimise IVF results by increasing the success rate through transferring only chromosomally healthy embryos.
- Advanced maternal age.
- Recurrent miscarriage.
- Implantation failure.
- Previous unsuccessful assisted reproduction treatments.
- Severe male factor or abnormal sperm FISH results.
- When one or both partners are carriers of a genetic disease or another hereditary condition.
- Couples with previous pregnancies affected by an abnormal number of chromosomes.
