Chorionic Villus Sampling Health Article

Definition

Chorionic villus sampling (CVS) is a prenatal procedure for the removal by needle of chorionic villi and culture and examination of the fetal cells obtained. The cells are used in tests for genetic and chromosomal abnormalities of a fetus as early as 10 to 12 weeks of gestation.

Purpose

Women who are at risk of carrying a fetus with a genetic or chromosomal defect may be counseled to have a prenatal screening test such as CVS or amniocentesis. CVS, which is performed at 10 to 12 weeks after a woman's last menstrual period, may be offered as an alternative to amniocentesis, the more commonly used test for prenatal diagnosis of genetic disorders, which is performed usually at 15 to 18 weeks. Earlier diagnosis of congenital defects is especially beneficial in cases where the parents' desire to know the results as early in preg- nancy as possible, for instance, when therapeutic abortion is being considered, as the risks associated with abortion increase with gestational age.

Prenatal screening can diagnose some genetic and virtually all chromosomal disorders and is advised for women who have one or more of the following risk factors:

• Women age 35 and older. The chance of having a child with certain chromosomal birth defects increases with maternal age. The most common chromosomal disorder is Down syndrome, a combination of mental and physical abnormalities caused by the presence of an extra copy of chromosome 21. The occurrence of Down syndrome in children born to women in their 20s is approximately 1 in 1,250, but increases to 1 in 400 by age 35, and to 1 in 100 at age 40.
• A child or previous pregnancy with a birth defect, or a history of miscarriages. A woman who has already had a child or pregnancy diagnosed with a genetic birth defect or chromosomal abnormality, or who has had multiple miscarriages, is at increased risk of having a child with a genetic disorder.
• Determination of the sex of a fetus when the mother is known to be a carrier of a sex-linked genetic disease (for example, hemophilia A).
• Other family history of genetic disease. Couples who do not have an affected child but who have family medical histories of genetic or chromosomal abnormalities or are known through genetic screening to be carriers of an inherited disease are at increased risk of having an affected child. Prenatal testing is offered only when the suspected condition can be diagnosed before birth.