Embryos can be tested for abnormal chromosomes before they are transferred to the uterus. This is called preimplantation genetic testing, PGT. It is done in a lab, using in vitro fertilization (IVF). One or more cells from each embryo is sent for genetic testing. Genetically healthy embryos are later transferred to the uterus, where they may attach to its lining and produce a healthy pregnancy.
One or more cells are taken from an embryo and sent for genetic testing while the embryo is growing in the IVF laboratory. The testing can be done at different stages using different techniques. Our lab offers PGD, PGS for 5 chromosomes (13, 18 21, X, Y) and PGS 24 (all chromosomes).
PGD involves testing an embryo before it implants for a specific, known genetic disorder. PGS involves testing an embryo for chromosomal abnormalities. Many embryos with chromosomal abnormalities will not lead to a pregnancy, or will result in a miscarriage. The percentage of embryos that are abnormal can be affected by many factors, including the age and health history of the parents.
On Day 3 or Day 5 of embryo development, the embryologist will carefully remove a single cell from the 8 cells stage embryo or a 5-10 cells blastocyst stage embryo. Only embryos that contained 6, or more cells on Day 3, or a good quality blastocyst on Day 5 will be tested.
The chance of the embryos being damaged during the biopsy procedure is very low (about 1%). However, it has not been determined if some undetected damage may result in an increased risk of obstetric complications, fetal abnormalities, or may decrease the chance of achieving a pregnancy. Also, the diagnosis may be made on an embryo that is incorrect. Some embryos may contain cells that are genetically normal and, within the same embryo, other cells which are abnormal. This is called mosaicism. It may result in the transfer of an embryo carrying an abnormal chromosome or genetic abnormality or the failure to transfer a normal embryo.