Most women will have normal, healthy babies and will not require Chronic Villus Sampling Chorionic villus sampling (CVS) or other invasive prenatal tests. However, all couples have a 3 percent chance of having a child with a birth defect and a physician may recommend CVS, a procedure to obtain a small amount of tissue (chorionic villi) from the developing placenta of the fetus for the purpose of genetic testing in order to learn more about the babies’ risk for a birth defect.
A CVS is performed under ultrasound guidance by passing a needle through the mother’s abdomen or through the cervix to reach the placenta. The procedure is performed as an outpatient and the mother is generally advised to decrease activity the day of the procedure and return to normal activities the following day.
A doctor may offer Chorionic villus sampling for a patient’s consideration when:
- When a woman is concerned about her risk of chromosome abnormalities
- There is a history of genetic disorders or a concerning family history
- Parent(s) are known to be carriers of a genetic condition
- An early ultrasound anomaly is detected
Typically Chorionic villus sampling is performed between the 11th and 13th week of pregnancy, and the results are usually available in 1-2 weeks.
A CVS is performed in one of two ways. The method used is typically dependent on the position of the uterus and the location of the placenta within the uterus.
- Transabdominal – this method involves passing a needle through the mother’s abdomen into the placenta under ultrasound guidance, and withdrawing some cells of the placenta into the needle with a syringe. An anesthetic to numb the skin may be used with the procedure.
- Transcervical – this involves passing a small catheter through the cervix into the uterus and withdrawing some cells of the placenta. This method is also performed under ultrasound guidance.
Cells taken by CVS can be tested for chromosome abnormalities that include Down syndrome (Trisomy 21), or genetic conditions such as Tay-Sachs Disease and Sickle Cell Disease. CVS is not an appropriate test for families with a history of neural tube defects (i.e., spina bifida), as such defects are not detected by CVS. CVS can only detect a small number of specific genetic or chromosomal problems, and it’s important for parents to understand that no prenatal test is 100 percent accurate.
There are some risks associated with Chorionic villus sampling. Some women may experience cramping, spotting or discomfort after the procedure, and there is a slightly higher risk for miscarriage. There have been a few reports of limb and jaw defects in infants whose mothers had CVS. Most of these mothers had CVS performed very early in pregnancy (before 10 weeks), and large studies have not found an association with fetal birth defects when CVS is performed after 10 weeks; however, the possible association of CVS with these specific birth defects remains controversial.
Louise E. Wilkins-Haug, MD, PhD, is the Division Director of Maternal Fetal Medicine and Reproductive Genetics at Brigham and Women’s Hospital