Genetics at a glance
- Genes are the governing elements in DNA that determine a human’s development, function, and personal characteristics.
- Genetic disorders and diseases are introduced when the normal DNA sequence is changed in part or in whole, caused by mutation in one or multiple genes.
- During the in vitro fertilization (IVF) process, embryos can be tested for genetic disorders or conditions through preimplantation genetic diagnosis (PGD) or screening (PGS).
- Aneuploidy screening looks for a specific set of chromosomes that contribute to recurrent miscarriages to make sure they are normal, which can be done during PGD.
About Genetic Disorders
Genes are the governing elements in DNA (deoxyribonucleic acid) that determine a human’s development and function, affecting personal characteristics like hair and eye color, blood type, and susceptibility to disease. Genetic disorders and diseases are introduced when the normal DNA sequence is changed in part or in whole, caused by mutation in one or multiple genes, mutations combined with environmental factors, or damaged chromosomes (number or structure changes to entire chromosomes, which carry the genes).
Some genetic diseases are mutations present at birth (inherited from parents), such as sickle cell disease. Some genetic mutations are acquired during a person’s lifetime, are affected by environmental exposures (such as cigarette smoke) or occur randomly.
Embryo genetic testing
During IVF, a woman’s egg is fertilized and the embryos grow for several days. On the third day, healthy embryos are usually at the six or eight cell stage, so one cell is removed from each viable embryo to be biopsied and analyzed for genetic diseases and disorders. The embryo can compensate for the loss of one cell, and it has been proven to not interfere with embryonic development. One or more of the embryos that are found to be disease free are then transferred to the woman’s uterus.
Since there is a known error rate for preimplantation genetic diagnosis (PGD), it is recommended that common methods of prenatal testing like chorionic villus sampling (CVS) and amniocentesis be performed in addition to PGD to eliminate any risk of misdiagnosis.
Aneuploidy screening looks for a specific set of chromosomes that contribute to recurrent miscarriages to make sure they are normal, which can be done during PGD and PGS (preimplantation genetic screening). The most common chromosomal abnormalities linked to pregnancy loss include:
- trisomy (three copies of a chromosome)
- monosomy (one copy of a chromosome) for chromosomes 13, 15, 16, 18, 21, or 22
- triploidy (three copies of all the chromosomes)
- sex chromosomes abnormalities
As with embryo testing, aneuploidy screening requires ovarian stimulation, egg harvesting, lab fertilization, embryo culture, and embryonic cell sampling. The cell removed from each embryo is tested for number of chromosomes or for a specific chromosome disorder. Only embryos that test normal are transferred to the uterus, increasing chances of a healthy pregnancy.