Prenatal Genetics Testing
It’s not uncommon to seek reassurance about your pregnancy. Generation® Prenatal Genetics Testing involves testing the fetus before birth to determine whether the fetus has certain abnormalities. This can include spontaneous genetic disorders as well as inherited disorders (see Generation® Genetic Carrier Screening).
What is a Chromosome Abnormality?
Most of us have 46 chromosomes in every cell of our bodies with half coming from each parent. The DNA within these chromosomes contributes to our development and health. Chromosome structures with extra or missing pieces, or other alterations can cause major birth defects, mental retardation and genetic syndromes.
- Conditions Caused by Chromosome Abnormalities – Babies with changes in their chromosomes may have mild to severe mental retardation and/or birth defects. The most common chromosome abnormality is Down syndrome.
- Chromosome Tests – A chromosome test is performed on fetal cells in the amniotic fluid or chorionic villi (placental cells) to determine if the fetus has a chromosome abnormality. The test also detects the gender of the fetus. You may choose whether or not you want to know the gender of your baby.
- How Abnormalities Occur – Most chromosome abnormalities happen at conception when an abnormal sperm or egg from one parent containing extra or missing genetic material comes together with a normal sperm or egg from the other parent. Abnormal sperm or eggs are present in everyone, and have nothing to do with what the parents did or did not do. We do know the chance of a chromosome abnormality increases with the mother’s age.
There are choices for how to screen in pregnancy
Prenatal Testing Options – Today, prenatal testing is part of nearly every pregnancy. Benefits and limitations of the commonly offered prenatal genetic tests are discussed below:
I. Prenatal Screening
- Benefits: A simple non-invasive blood test (often combined with an ultrasound). The test is safe with little risk to the mom or fetus. Cost is reasonable.
- Limitations: These tests offer high accuracy, but are less accurate than prenatal diagnostic tests like CVS or amniocentesis. Multiple visits can be necessary if the blood draw and ultrasound are performed separately.
II: Non-Invasive Prenatal Testing (NIPT)
- Benefits: Simple non-invasive blood test coupled with extremely high accuracy (up to or greater than 99%). NIPT tests are marketed under several brand names.
- Limitations: As a new test, NIPT can be costly if not covered by insurance.
- To learn more, visit the NIPT page.
III. Prenatal Diagnosis (Amniocentesis and CVS)
- Benefits: Amniocentesis and CVS traditionally deliver the most accurate results (>99%). These tests are typically offered to mothers who have an increased risk for an abnormality, for example, the mother’s age.
- Limitations: These invasive tests carry a slight risk to the pregnancy. Amniocentesis draws a small sample of amniotic fluid from the uterus. CVS draws a small sample of cells from the placenta. These tests are costly, but are established diagnostic tests typically covered by insurance.
Information about CVS
Chorionic villus sampling, or CVS, is a diagnostic genetics test in which a small sample of tissue (the chorion ) is removed from the placenta to determine the health of your fetus. It is performed in early pregnancy, usually between 10 weeks and 13 weeks.
Who should undergo CVS?
CVS is recommended to women with a higher than average risk to deliver a child with a genetic condition. These include women over the age of 35, a prior birth involving or family history of a genetic condition such as Down syndrome or cystic fibrosis, an abnormal finding on an ultrasound, or if either parent carries a genetic condition. CVS is currently not performed at our facility, but appropriate referrals can be made, if desired.
How is ultrasound used as part of a genetic test?
With the ultrasound we are able to measure the nuchal translucency (NT) of the baby. The purpose of the NT is to measure the thickness of the fluid collection at the back of the baby’s neck. This ultrasound is typically performed between 11 weeks, 2 days to 13 weeks, 6 days. The ultrasound assesses your baby’s risk of having a genetic abnormality and in some cases may indicate a risk for congenital heart problems.
At what stage is the ultrasound given?
In addition to the NT (nuchal translucency) screening performed between 11 and 14 weeks, ultrasound may be performed at various stages throughout pregnancy, including anatomy scan at approximately 20 weeks to assess fetal development.
How should I prepare for my ultrasound?
We have a few suggestions to help your ultrasound be as quick and comfortable as possible. 1) Bring 20 ounces of water to begin drinking upon arrival 2) Eat a full meal within 30 minutes to 1 hour before your appointment 3) Bring a snack to assist with fetal activity during the ultrasound, if needed.
For information regarding our other prenatal services, click here for The Center of Medical Genetics website.