Genetic testing can be performed at two crucial stages in a couple’s journey towards parenthood: before pregnancy or before the transfer stage of an IVF cycle.
Pre-Pregnancy Genetic Screening
Pre-pregnancy genetic screening may help identify couples who have an increased risk of age-related or familial genetic disorders and birth defects. No single test, however, can accurately predict the risk of all defects in a child, and many birth defects, such as those related to environmental and toxic exposures and those that are random and unexplained, are not genetically based and may not be detected with genetic screening.
Pre-pregnancy genetic testing on both parents is a simple saliva test that determines if either or both parents are carriers for a number of hereditary diseases. If testing shows that both parents are carriers of a gene mutation then they can pass this disease on to their children. Because this testing occurs before pregnancy, couples can make informed decisions regarding their future family.
Screening for genetic diseases that may affect offspring depends upon the racial or ethnic background of the couple, their family and medical history, and associated conditions. Various racial and ethnic groups demonstrate an increased prevalence of specific diseases, and couples of these backgrounds may have their carrier status screened accordingly, as described below. Most couples have their carrier status checked if there is a family history of the disorder or if they belong to an at-risk racial or ethnic group.
Genetic Testing of Embryos
The second type of genetic testing occurs during an IVF cycle either on the fertilized embryos before they are transferred back to the uterus. Two options for pre-implantation genetic testing are PGT and PGD.
Pre-implantation Genetic Testing (PGT) helps to answer the question of which embryos have the greatest potential to become a healthy pregnancy and baby. Aneuploidy occurs when an embryo has too many or too few normal chromosomes and occurs most frequently at the time of fertilization in humans. It is a major cause of miscarriage and increases dramatically with maternal age. To test for aneuploidy in embryos, a few cells are taken from the outer layer of the embryo during an IVF procedure and screened for chromosomal abnormalities.
PGT gives the patient two advantages: 1) 99% certainty the embryo has the correct number of chromosomes, thereby increasing the chance for a healthy pregnancy and 2) transfer of only ONE embryo thereby dramatically decreasing the chance of multiple gestations. The pregnancy rate following transfer of just one normal screened embryo is the same as that following transfer of two unscreened embryos.
Some couples request an extension of this technology, also known as Pre-implantation Genetic Diagnosis (PGD), to detect specific genetic conditions that may run in their families, such as Tay-Sachs disease, cystic fibrosis, muscular dystrophy, Fragile X syndrome or spinal muscular atrophy. Couples who have done pre-pregnancy genetic testing resulting in positive carrier status often elect to perform PGD on their oocytes or embryos during an IVF cycle.