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Amniocentesis and chorionic villus sampling (CVS) are diagnostic tests available in pregnancy. They are performed under ultrasound guidance as an outpatient procedure. CVS and amniocentesis are associated with a small (less than 1 percent) risk of miscarriage.

What tests are performed on the CVS or amniocentesis sample?

The tests that are performed vary based on your indication to have diagnostic testing. If both you and your partner are found to be carriers of the same genetic disorder (i.e. cystic fibrosis), testing would be performed to test the fetus for the known gene changes (mutations) in each of you. Chromosome testing the fetus is often performed to rule out Down syndrome or another chromosome abnormality. The genetic counselor would also discuss the option of a newer test, called microarray. Microarray testing can detect extra or missing copies of regions of chromosomes. Microarray testing is most useful for patients whose pregnancy shows abnormalities on ultrasound. A genetic counselor can discuss the benefits, limitations, and pitfalls of microarray testing.

How is amniocentesis performed?

Amniocentesis is performed by inserting a long thin needle through the abdomen and into the uterus to remove a small amount of the amniotic fluid surrounding the fetus. A variety of tests can be performed on the cells in the fluid and the fluid itself.

How is CVS performed?

CVS is done by inserting a long thin needle through the abdomen and into the placenta to remove a sample of placental tissue fragments. Alternatively, a small catheter is inserted through the cervix into the placenta to remove a sample.

What if amniocentesis or CVS shows that my baby will have a birth defect?

If your baby is found to have a serious birth defect, you will receive counseling about what this will mean for the infant, you and your family. The genetic counselor and your doctor will provide you with information about what options are available during and after pregnancy.

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