Preimplantation Genetic Testing (PGT)

In IVF, eggs are fertilised in the laboratory and the embryos grow for several days. By day 5 to 7, a developing embryo becomes a blastocyst, with an inner cell mass that will form the baby and an outer layer, the trophectoderm, that will form the placenta. In PGT, an embryologist removes a few cells from this outer layer with a fine laser and pipette, a step called trophectoderm biopsy, and the embryo is then vitrified. The cells go to a genetics laboratory. PGT-A, for aneuploidy, counts the chromosomes to find embryos with missing or extra copies, which usually fail to implant or miscarry and in some cases, such as Down syndrome, lead to a chromosomal condition. PGT-M, for monogenic conditions, tests for a particular gene change known in the family, such as cystic fibrosis, thalassaemia or Huntington disease. PGT-SR, for structural rearrangements, looks for unbalanced chromosome segments when a parent carries a translocation or an inversion.

PGT-M is recommended when one or both partners carry a known gene change that can cause a serious inherited condition, for example when both partners carry the same recessive condition, or one carries a dominant or X-linked condition. PGT-SR is recommended when a parent carries a balanced chromosome rearrangement, which often comes to light through recurrent miscarriage or a previous affected pregnancy. PGT-A is the most debated. It is sometimes offered to women of older reproductive age, to couples with recurrent miscarriage or repeated failed implantation, or to help choose a single embryo for transfer, but research has not shown that it increases the overall chance of a baby from an IVF cycle for most patients; its main effect is to reduce the number of transfers and miscarriages along the way. Some countries also restrict which indications are allowed. A fertility specialist and a genetic counsellor should discuss whether PGT is useful in your situation.

PGT is part of an IVF cycle. For PGT-M and PGT-SR, the genetics laboratory first prepares a test tailored to your family, using blood or saliva samples from you, your partner and sometimes relatives, and this work-up can take several weeks to a few months. Ovarian stimulation and egg collection then follow the usual IVF steps, and the eggs are fertilised, usually by ICSI so that no stray sperm DNA contaminates the sample. Embryos are cultured to the blastocyst stage, and each embryo that reaches it is biopsied on day 5, 6 or 7 and then frozen. The laboratory analyses the cells, usually by next-generation sequencing, and reports on each embryo within about 1 to 3 weeks. After genetic counselling on the results, a single suitable embryo is warmed and transferred to the uterus in a later frozen embryo transfer cycle, a quick procedure similar to a cervical smear that needs no anaesthesia.

PGT suits people undergoing IVF who have a known genetic risk, a balanced chromosome rearrangement or, after counselling, a selected reason for PGT-A. Because only embryos that reach the blastocyst stage can be tested, the approach works well only when enough eggs can be collected; with very few eggs there may be no embryo to test or transfer. Preparation includes the usual IVF assessments, such as ovarian reserve tests, semen analysis and infection screening, plus genetic reports confirming the exact gene change or rearrangement for PGT-M or PGT-SR. Genetic counselling before treatment explains what can and cannot be detected, the chance that no suitable embryo is found, and how mosaic or unclear results will be handled. International patients should send genetic reports early, because designing a PGT-M test takes time, and should confirm that the planned indication is legally permitted where treatment happens and how frozen embryos can be stored or moved later.

PGT itself needs no physical recovery, because the biopsy is done on the embryo, not on you. Recovery is that of egg collection: a few hours of rest, mild cramping and bloating for a few days, and usually a return to normal activity the next day. Because embryos are frozen after biopsy, treatment naturally splits into two visits. The first covers stimulation and egg collection, about two weeks, and you can usually fly home 1 to 3 days after collection. The results arrive while you are at home, and a genetic counselling call explains them. The second visit, for the frozen embryo transfer, is shorter: the uterus is prepared with hormones, often with monitoring near home, and you travel for the transfer itself, staying a few days if you wish. A pregnancy test follows about 9 to 11 days after transfer, often near home. Tests during pregnancy should be planned with your home obstetrician.

The biopsy removes only cells destined to form the placenta, and studies of children born after PGT have not shown a clear increase in health problems, although long-term follow-up continues. The surrounding procedures carry the usual IVF risks, mainly ovarian hyperstimulation syndrome and small risks from egg collection. The main limits lie in the results. Some embryos are mosaic, containing a mix of normal and abnormal cells; a biopsy may not reflect the whole embryo, and mosaic embryos can sometimes lead to healthy babies, so they are discussed individually rather than automatically discarded. Testing can rarely give a wrong result, and PGT checks only for what it is designed to detect, so it cannot exclude every genetic or developmental condition. Some cycles produce no suitable embryo. For these reasons, screening or diagnostic tests in pregnancy are still recommended. PGT can lower the chance of an affected pregnancy and of miscarriage from chromosomal causes, but it cannot ensure a healthy baby.