Chorionic Villus Sampling (CVS)
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|What Is The Test And Why Was I Recommended To Take it?
If you receive an abnormal result from a routine prenatal blood test, a chorionic villus sampling (CVS) may be recommended by your healthcare provider (image). It is a diagnostic test, which means it can be used for diagnosing the presence of a condition (by comparison a routine screening can only indicate a possible problem which needs further investigation). A CVS involves taking a tiny sample of placenta tissue during early pregnancy to test for signs of genetic defects in the developing embryo. It can be used to detect hundreds of disorders including Down syndrome, sickle cell anemia, cystic fibrosis, Turner syndrome, Klinefelter syndrome and Tay-Sachs (see prenatal tests).
A CVS is performed in week 10 to 13 of pregnancy. Its main advantage over an amniocentesis test is that it can be performed earlier in the first trimester of pregnancy. This means a woman can hopefully receive reassuring results sooner. An amniocentesis in comparison is usually performed between weeks 16 and 18 of pregnancy. With a CVS procedure, the doctor takes cells from tiny fingerlike projections on the placenta called the chorionic villi and sends them to a lab for genetic testing. The earlier the diagnosis of disorders, the more helpful it is for couples who might want to consider a therapeutic pregnancy termination. An early abortion procedure is considered less traumatic and complicated than a later one.
Chorionic villus sampling does not detect neural tube defects such as spina bifida. If neural tube defects are suspected, an amniocentesis will be performed instead. Your healthcare provider will explain all the options to you, and may recommend seeing a genetic counselor prior to any procedure. They can advise women on genetic testing in pregnancy.
CVS procedures are usually performed in hospital, although they may be carried out in the OB/GYN's surgery. You may be asked to drink fluids and refrain from urinating before the procedure as a full bladder allows better visualization on the pregnancy ultrasound scan. Depending on the location of the placenta, a sample of cells is taken via the vagina and cervix (transcervical) or via a needle inserted into the abdominal wall (transabdominal CVS). Neither method is pain free and discomfort can range from mild to moderate. Some women say the transcervical test feels like a Pap smear test. Ultrasound is used to help guide the direction of the tube (in the case of a transcervical) or the direction of a needle in the case of a transabdominal. If your blood is Rh negative, you may receive special immune globulins, called RhoGAM to prevent Rh incompatibility. The sample taken is then sent to a lab and used to study the chromosomes, DNA and any signs (called chemical markers) of disease in the developing baby. CVS is able to accurately detect chromosomal abnormalities 98 percent of the time.
CVS is a safe and reliable diagnostic test and studies show the risk of pregnancy complications such as miscarriage following the procedure is about 1 in 370 (which is almost twice the risk associated with an amniocentesis). The risks are slightly higher if it is carried out through the cervix as opposed to the through the abdomen. Risks can be reduced by waiting until after the 10th week of pregnancy and choosing a hospital with a good safety record. Some women experience vaginal bleeding after a CVS, but it is not cause for great concern, although it should be reported to their OB/GYN (particularly if it lasts longer than 3 days). As there is also a slight risk of infection with a CVS, any rise in temperature or fever should be reported immediately. There have been some concerns that CVS may be associated with limb defects in babies, such as missing toes and fingers. However, these incidences mainly occurred in women who tested before week 10 of pregnancy. Current research suggests that there is no increased risk for women who have a CVS at week 11 or later.
The American College of Obstetricians and Gynecologists now recommends pregnant women of all ages be offered first and second trimester screening and recommends informing women of relevant diagnostic testing options. Your OB/GYN or genetic counselor will discuss the various options available to you, but ultimately the decision go beyond the regular screening and take diagnostic tests is a personal one. The majority of women opt for routine prenatal screening and only then make a decision on diagnostic testing when they receive the results. Other women decide to go for diagnostic testing straight away because they suspect or know that they are at high risk of chromosomal problems. Some women who opt for invasive genetic testing are clear in advance that if a serious problem is indicated they will terminate their pregnancy. On the other hand, some women refuse diagnostic testing because of the (limited) fear of miscarriage or because they do not believe in terminations, so there is no obvious benefit to testing.
Including physician fees, a test can range between $1,400 to $2,000. It is also common to pay a premium if you would like the results faster. Some insurance plans cover the cost of a chorionic villus sampling, especially where the mother is over 35 years of age. You may need to provide your insurance company a referral from your healthcare provider.
For more about prenatal screening, see the following:
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