(CVS, Chorionic Villus Biopsy)
What is chorionic villus sampling?
Chorionic villus sampling (CVS) is a prenatal test that involves taking a sample of tissue from the placenta, a structure in the uterus that provides blood and nutrients from the mother to the fetus, to test for chromosomal abnormalities and certain other genetic problems.
The chorionic villi are tiny projections of placental tissue that look like fingers and contain the same genetic material as the fetus. Testing may be available for other genetic defects and disorders depending on the family history and availability of lab testing at the time of the procedure.
CVS is usually performed between the 10th and 12th weeks of pregnancy. Unlike amniocentesis (another type of prenatal test), CVS does not provide information on neural tube defects, such as spina bifida. For this reason, women who undergo CVS also need a follow-up blood test between 16 to 18 weeks of their pregnancy to screen for neural tube defects.
There are two types of CVS procedures:
Transcervical - a catheter is inserted through the cervix into the placenta to obtain the tissue sample
Transabdominal - a needle is inserted through the abdomen and uterus into the placenta to obtain the tissue sample
Another related procedure that may be used to diagnose genetic and chromosomal defects is amniocentesis. Please see this procedure for additional information.
Anatomy of the fetus in utero:
Amniotic sac - a thin-walled sac that surrounds the fetus during pregnancy. The sac is filled with amniotic fluid (liquid made by the fetus) and the amnion (the membrane that covers the fetal side of the placenta), which protects the fetus from injury and helps to regulate the temperature of the fetus.
Anus - the opening at the end of the anal canal
Cervix - the lower part of the uterus that projects into the vagina. Made up of mostly fibrous tissue and muscle, the cervix is circular in shape.
Fetus - an unborn baby from the eighth week after fertilization until birth
Placenta - an organ, shaped like a flat cake that only grows during pregnancy and provides a metabolic interchange between the fetus and mother. (The fetus takes in oxygen, food, and other substances and eliminates carbon dioxide and other wastes.)
Umbilical cord - a rope-like cord connecting the fetus to the placenta. The umbilical cord contains two arteries and a vein, which carry oxygen and nutrients to the fetus and waste products away from the fetus.
Uterine wall - the wall of the uterus
Uterus (Also called the womb.) - the uterus is a hollow, pear-shaped organ located in a woman's lower abdomen, between the bladder and the rectum, that sheds its lining each month during menstruation and in which a fertilized egg (ovum) becomes implanted and the fetus develops
Vagina - the part of the female genitals, behind the bladder and in front of the rectum, that forms a canal extending from the uterus to the vulva
Reasons for the procedure
Chorionic villus sampling may be used for genetic and chromosome testing in the first trimester of pregnancy in the presence of one or more of the following conditions:
Family history or previous child with a genetic disease, or chromosomal or metabolic disorder
Maternal age over 35 years by the pregnancy due date
Risk of a sex-linked genetic disease
Previous ultrasound with questionable or abnormal findings
There may be other reasons for your physician to recommend a chorionic villus sampling.
Risks of the procedure
As with any invasive procedure, complications may occur. Some possible complications may include, but are not limited to, the following:
Cramping, bleeding, or leaking of amniotic fluid
Limb defects in infants, especially in CVS procedures done before 9 weeks (rare)
Patients who are allergic to or sensitive to medications or latex should notify their physician.
Women with twins or other multiples will need sampling from each placenta in order to study each baby.