Genetic Screening

If you are over 35, have a family history of genetic diseases, or have a previous child with a genetic disorder, it is likely that your doctor will recommend that you have genetic screening done either before or during your next pregnancy. In this article we’ll give you a brief overview of the different types of genetic testing available, and what they screen for.

Test Performed Before Pregnancy
Carrier identification is genetic testing that will let you know if you carry any genetic disorders that you could pass onto your offspring, or that make you more susceptible to certain diseases or disorders.

Carrier identification can be done on any person at any age, not just pregnant women, using a blood sample, which is analyzed for specific genetic markers. The most common reason for testing is because a person’s family has a history of a certain disorder, or a couple has a previous child with a birth defect, such as cystic fibrosis, sickle cell anemia or Tay-Sachs disease.

Tests Performed During Pregnancy
Common genetic testing performed on the mother while she is pregnant are:

Test How/When it’s Done What it Tests For
Amniocentesis Uses a long needle to take a sample of amniotic fluid from the sac surrounding the fetus. Usually done around week 16. Test looks at the levels of alpha fetoprotein (AFP), which can indicate neural tube defects, such as spina bifida, or chromosomal defects. Can also determine the sex of the baby.
Maternal Serum Screening A sample of the mother’s blood is taken to check the levels of alpha fetoprotein (AFP). Usually done between weeks 15 and 19 of the pregnancy. Levels can indicate neural tube defects, or chromosomal defects.
Chorionic Villus Sampling A sample of the tissues that attaches the amniotic sac to the uterine wall, called the chorionic villi, is taken. Only offered in the case of high risk pregnancy because of increased risk of miscarriage. If the test is done it will be between weeks 10 and 12. Tests for Down syndrome, and other physical and mental defects that can be caused by the presence of an extra chromosome.

Tests Performed on the Fetus
Fetal blood sampling, also known as Percutaneous umbilical blood sampling (PUBS), is the genetic test commonly performed on a fetus while it is still in-utero. To do the test, a sample of blood is taken from a fetal blood vessel, using an ultrasound as a guide. It is then tested for fetal infections, fetal oxygen levels, anemia, Rh disease and other blood diseases. This method can also be used to administer medications to the fetus.

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