A First Trimester Prenatal Test
Chorionic Villus Sampling
A prenatal test called Chorionic Villus Sampling - may be offered to you during the
course of your pregnancy. Chorionic Villus Sampling - also called CVS or Chorionic Villi
Sampling - is performed
during the first trimester of pregnancy.
So what is this test for?
More importantly, is it safe?
Is it accurate?
Chorionic Villus Sampling
Chorionic Villus Sampling is a prenatal test designed to identify chromosome abnormalities in your baby - for example: Down's Syndrome
and other inherited disorders such as cystic fibrosis.
Some Chorionic Villi cells are removed from your placenta at the point where it attaches to the uterine wall.
Vocabulary
What are Chorionic Villi?
They are tiny finger-shaped growths found in your placenta. The genetic
material in chorionic villus cells is the same as that of your baby's cells.
What is cystic fibrosis?
It is a hereditary disease that affects the exocrine (mucus) glands of the lungs, liver, pancreas,
and intestines, causing progressive disability due to multisystem failure.
Prenatal Test: How Are Samples Collected?
There are two ways in which samples are collected:
Transcervical: An
obstetric ultrasound guides a thin catheter through your
cervix
to your placenta. The chorionic villi cells are gently suctioned into the catheter. This is the most common method.
Transabdominal: An ultrasound guides a long thin needle through your abdomen to your placenta. The needle draws a sample of
tissue and then is removed. This procedure is similar
to that of amniocentesis.
The CVS procedure collects larger samples and provides faster results than amniocentesis.
Results may be received between one to seven days after you have taken the test.
CVS is usually performed between 10 and 13 weeks of gestation.
How is CVS Different Than Other Genetic Prenatal Testing?
Vocabulary
What is Spina Bifida?
It comes from the Latin: "split spine."
It is a developmental birth defect involving
the neural tube. It is the incomplete closure of
the embryonic neural tube resulting in an incompletely formed spinal cord.
In addition, the vertebrae overlying the open
portion of the spinal cord do not fully form and remain unfused and open. This allows the abnormal portion of
the spinal cord to stick out through the opening in the bones.
There may or may not be a fluid filled sac surrounding the open spinal cord.
This prenatal test is different from amniocentesis in that it does not allow for testing for neural tube defects - i.e. Spina Bifida.
Chorionic villus sampling also provides access to DNA for a prenatal paternity test prior to delivery.
CVS is said to have a high levels of accuracy: 98-99%.
Although the probabilities of identification are high, this test does not measure the severity of the disorders it tests for.
For example, if your baby has cystic fibrosis, CVS cannot tell you the severity of this disease.
Is This a Dangerous Prenatal Test?
CVS is recognized as an invasive prenatal screening test that does pose potential risks.
Pregnancy loss is the primary risk related to CVS occurring 1 out of every 100 procedures.
It carries a higher risk than amniocentesis.
CVS is not recommended for women who:
Have an active infection - i.e. STD (sexually transmitted disease)
Are carrying twins
Have experienced vaginal bleeding during pregnancy
Following the procedure, you may experience one or more of the following side effects:
Infection
Spotting
Cramping and/or pain at puncture point
Fever
Chills
Leaking of amniotic fluid
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Prenatal Test: Reviews
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Resources:
Mayo Clinic Complete Book of Pregnancy and Baby's First Year. Johnson, Robert V., M.D., et al, Ch. 11.
http://www.americanpregnancy.org/prenataltesting/amniocentesis.html
Williams Obstetrics Twenty-Second Ed. Cunningham, F. Gary, et al, Ch. 13.
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