Genetic Testing and Pregnancy
When is carrier screening done?
Ideally you should be screened prior to starting a family, but the tests can also be done after conception, preferably as soon as you learn of your pregnancy.
Thanks to advances in genetic research, an increasing number of recessive genetic disorders can be detected through carrier screening. Many of these disorders are rare in the general population but more common in certain ethnic groups.
Cystic Fibrosis, Spinal Muscular Atrophy and Fragile X syndrome are three genetic disorders that occur more frequently in the general population. It is recommended that carrier screening for these disorders be offered to all prospective parents.
Whether you should consider additional tests depends on your ethnic background and family medical history.
- Ashkenazi Jews have a higher carrier frequency for Tay-Sachs and 16 other genetic diseases. The Ashkenazi panel was developed to screen for all these disorders with one blood test. (90% of American Jews are Ashkenazi.)
- People of Irish, British, French Canadian, or Cajun background have an increased risk of Tay-Sachs.
- Certain genetic disorders affecting the red blood cells are more common among people of Asian, African, or Mediterranean descent.
- A family history of miscarriages, children with developmental delays, or children who died young could indicate a genetic disorder running in your family.
If any of these risk factors applies to you or your partner, you should ask your physician about carrier screening, preferably before you become pregnant. Genetic diseases are rare in the general population, and the subject may not come up in conversations with your physician unless you mention it. Make sure you know your family medical history and tell your physician about your risk factors.
Generally both parents are tested. Depending on your particular sitation, you and your partner may be screened simultaneously or one at a time. Your healthcare provider takes a sample of your blood and sends it to a lab where it is analyzed for evidence of genetic abnormalities. Results take approximately 2 weeks.
If one parent tests positive for a an autosomal recessive disorder but her partner tests negative, the couple's child will not be born with the disease, though the child still has a 50% of being a carrier.
If the woman tests positive for an X-linked disorder such as Fabry Disease, her child has a 50% chance of inheriting the gene mutation for that disorder, since all children inherit one X chromosome from their mothers. A male child of a carrier mother will typically be affected by the disorder and a female child may or may not show symptoms (depending on the disease and/or mutation). Prenatal diagnostic testing is therefore recommended for pregnant women who are carriers of X-linked disorders.