Premiplantation Genetic Screening and Diagnosis
PGD at a glance
- Preimplantation genetic testing (PGD/PGS) is a test on an embryo to uncover genetic diseases that may be inherited from the parents.
- One or two cells are removed from the embryo and screened either for a specific genetic disease known to be present in the family or for a wide array of other genetic diseases.
- Embryos that are clear of the gene associated with a disease may be implanted.
- PGD may decrease the risk of genetic disease, but cannot completely eliminate it. Confirmation with amniocentesis is still necessary later on in a pregnancy.
Genetic testing can detect thousands of diseases such as Tay-Sachs, cystic fibrosis, muscular dystrophy, and sickle cell anemia.
Most Frequently Diagnosed Diseases and Disorders Detected by PGD and PGS:
- Cystic fibrosis
- Sickle cell anemia
- Spinal muscular atrophy
- Tay-Sachs Disease
- Huntington’s disease
- Hemophilia A
- Charcot-Marie tooth disease
- Fragile X syndrome
- Duchenne muscular dystrophy
- Myotonic dystrophy
Who should consider genetic testing
- Couples who have one child with a genetic problem.
- Couples who have suffered from three or more consecutive, spontaneous pregnancy losses due to genetic disorders.
- Maternal age of 35 or older.
- Women who have had two or more unsuccessful IVF cycles.
What Are The Benefits of Genetic Testing?
- To identify abnormal embryos and implant only those free of genetic disorders.
- To decrease the risk of passing on a serious genetic disorder from parent to child.
- To detect known genetic diseases or chromosomal abnormalities.
- To reduce multiple pregnancies by being able to identify competent embryos prior to transfer to a woman’s uterus.
Limitations of preimplantation genetic testing
- Using preimplantation genetic diagnosis (PGD) with in vitro fertilization (IVF) involves the same risks associated with IVF:
- Overstimulation of the ovaries causing pain and discomfort along with nausea, multiple pregnancy, and birth defects not related to the genetic test.
- Harm to the embryo from the biopsy or from freezing.
- False result, which would mean the transfer of an abnormal embryo to the uterus, resulting in either miscarriage or facing the decision of terminating the pregnancy. A false result could also cause discarding a normal embryo thought to be abnormal reducing the chance of a healthy pregnancy.
Alternatives to preimplantation genetic diagnosis (PGD)
At 10 to 12 weeks into a pregnancy, doctors can perform chorionic villus sampling (CVS). Another procedure is amniocentesis, which is performed 14 to16 weeks into a pregnancy, where amniotic fluid is removed and analyzed. Either test can diagnose fetal genetic abnormalities. In either test, if an abnormality is detected, the only options would be an abortion or carrying the fetus to term. Also, ultrasound with or without blood tests can be done during pregnancy. Typically the results of ultrasound are not specific, and may miss abnormalities. If abnormal results are obtained with ultrasound and/or blood tests, CVS or amniocentesis may also be recommended. Pre-screened donor eggs or donor sperm can be used to avoid the risk of inherited disease. There is also the option to choose not to do prenatal testing or genetic testing.