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DESCRIPTION
Chorionic villus sampling (CVS), also known as chorionic villus biopsy, is a prenatal diagnostic test performed on pregnant women who are at risk for carrying a fetus with a genetic or chromosomal or genetic defect. This test detects chromosomal and genetic abnormalities in a fetus. It involves the villi (hair-like projections) that compose the chorion (the outer layer of the amniotic sac). Cells from the villi provide chromosome information as do the cells from the amniotic fluid. A CVS test can be performed between the 9th and 12th weeks of pregnancy, providing earlier diagnosis than amniotic fluid studies. Although it carries a slightly higher risk, CVS may be used in place of amniocentesis for women who have one or more risk factors (see Reasons For Procedure).
Prenatal testing is often a topic of concern for parents-to-be. It is important to remember that most tests are negative, and positive results may open opportunities for successful interventions or informed choices. CVS may be chosen as the method of prenatal testing for those unable to have an amniocentesis, and those who may consider a therapeutic pregnancy termination in the case of birth defects. If the fetus has serious complications, an earlier abortion is often easier and safer than a second trimester abortion or possible second trimester miscarriage.
REASONS FOR PROCEDURE
CVS is not a routine test. It may be offered to pregnant women who have an increased risk of having a baby with a genetic birth defect that can be detected by CVS. These women include the following:
Mother is over age 35. Women age 35 and older have a higher chance of having a child with Down syndrome. This risk factor increases with maternal age. For instance, the chance of having a baby with Down syndrome is 1 in 378 for a 35-year-old woman and increases to 1 in 30 for a 45-year-old woman.
Pregnancy is considered high-risk. A history of miscarriages.
A blood test (AFP and Triple Screen) has suggested increased risk for chromosome abnormality.
Either parent has a chromosome abnormality or has a family history of genetic disease. Prenatal genetic testing is recommended if either the mother or the father of the unborn baby has a family history of genetic disease or is known to be a carrier of a genetic disease.
Mother has previously had a child with birth defects or chromosome abnormality, such as Down syndrome.
RISKS
Medical information states "none expected" (More information will be added as research continues). The degree of risk for the individual is often related to the skill and experience of the health care provider performing the procedure.
Updated Information:
Of women who undergo transcervical chorionic villus sampling, one third experience minimal vaginal spotting and 7-10% experience vaginal bleeding. One out of five women experience cramping following the procedure. Two to three women out of 100 (or 2-3%) will miscarry following chorionic villus sampling. The risk of infection is very low. Rupture of the amniotic membranes is a rare complication. Women with Rh negative blood may be at an increased risk for developing Rh incompatibility following chorionic villus sampling.
There have been reports of limb defects in babies following chorionic villus sampling. However, in 1996 the World Health Organization reported that the incidence of babies born with limb defects from 138,966 women who had undergone chorionic villus sampling was the same as for women who had not. Therefore, this study found no connection between chorionic villus sampling and limb defects. CVS safety studies continue. According to the University of Maryland Medical Center CVS sometimes causes birth defects in the limbs, for example, missing fingers and toes, and sometimes malformation in the tongue and jaw. These defects appear to be more common when CVS is performed earlier than the 10th week of pregnancy.
Chorionic villus sampling is not recommended for women who have vaginal bleeding or spotting during the pregnancy. It is not typically recommended for women who have Rh sensitization from a previous pregnancy.
DESCRIPTION OF PROCEDURE
Chorionic villus sampling has been in use since the 1980s. This prenatal testing procedure involves taking a sample of the chorion frondosum - that part of the chorionic membrane containing the villi - for laboratory analysis. The chorionic membrane is the outer sac which surrounds the developing fetus. Chorionic villi are microscopic, finger-like projections that emerge from the chorionic membrane and eventually form the placenta. The cells that make up the chorionic villi are of fetal origin so laboratory analysis can identify any genetic, chromosomal, or biochemical diseases of the fetus.
Chorionic villus sampling is best performed between 10 and 12 weeks of pregnancy. The procedure is performed either through the vagina and the cervix (transcervically) or through the abdomen (transabdominally) depending upon the preferences of the patient or the doctor. In some cases, the location of the placenta dictates which method the health care provider uses. Both methods are equally safe and effective. Following the preparation time, both procedures take only about five minutes. Women undergoing chorionic villus sampling may experience no pain at all or feel cramping or pinching. Occasionally, a second sampling procedure must be performed if insufficient villus material was obtained.
PREPARATION & PROCEDURE
Deciding to undergo prenatal genetic testing is a complex, personal decision. You may wish to consult with a genetic counselor to discuss the pros and cons of testing and how the test results may affect you and your family. Ask your health care provider to fully explain the benefits and risks of the procedure. Before having a CVS, your health care provider will ask you to sign a consent form.
Prior to the chorionic villus sampling procedure the woman needs to drink fluids and refrain from urinating to ensure her bladder is full. These preparations create a better ultrasound picture since a full bladder can help aid in the proper positioning of the uterus.
Ultrasound is used to determine the location of the fetus.
For the TRANSCERVICAL PROCEDURE, the woman lies on an examining table on her back with her feet in stirrups. The woman's vaginal area is thoroughly cleansed with an antiseptic, a sterile speculum is inserted into her vagina and opened, and the cervix is cleansed with an antiseptic. Using ultrasound (a device which uses sound waves to visualize internal organs) as a guide, the health care provider inserts a thin, plastic tube called a catheter through the cervix and into the uterus. The passage of the catheter through the cervix may cause cramping. The health care provider carefully watches the image produced by the ultrasound and advances the catheter to the chorionic villi. By applying suction from the syringe attached to the other end of the catheter, a small sample of the chorionic villi are obtained. Some women experience no pain with the transcervical CVS while others report feeling a pressure, a cramping or pinching feeling similar to a pelvic exam may be felt as the sample is being taken. The catheter is then easily withdrawn.
For the TRANSABDOMINAL METHOD, the woman lies on her back on an examining table. Ultrasound enables the health care provider to locate the placenta. The specific area on the woman's abdomen is cleansed thoroughly with an antiseptic and a local anesthetic may be injected to numb the area. With ultrasound guidance, a long needle is inserted through the woman's abdominal wall, through the uterine wall and to the chorionic villi. The sample is obtained by applying suction from the syringe. If the woman has a tipped uterus, the health care provider will generally choose the transabdominal method to minimize the risk of fetal harm or miscarriage. The risk of miscarriage is as high as 5 percent for a woman with a tipped uterus who undergoes transcervical CVS. The transabdominal may feel similar to a blood draw.
The chorionic villus sample is immediately placed into nutrient medium and sent to the laboratory. At the laboratory, the sample is examined under the microscope and any contaminating cells or material is carefully removed. The villi can be analyzed immediately, or incubated for a day or more to allow for cell division. The cells are stopped in the midst of cell division and spread onto a microscope slide. Cells with clearly separated chromosomes are photographed so that the type and number of chromosomes can be analyzed. Chromosomes are strings of DNA which have been tightly compressed. Humans have 23 pairs of chromosomes including the sex chromosomes. Rearrangements of the chromosomes or the presence of additional or fewer chromosomes can be identified by examination of the photograph. Down syndrome, for instance, is caused by an extra copy of chromosome 21. In addition to the chromosomal analysis, specialized tests can be performed as needed to look for specific diseases such as Tay-Sachs disease. Depending upon which tests are performed, results may be available as early as two days or up to eight days after the procedure.
Chorionic villus sampling costs are usually between $1,200 and $1,800. Insurance coverage for this test may vary.
ALTERNATE PROCEDURES
There are alternate procedures for diagnosing genetic and chromosomal disorders of the fetus. Amniocentesis is commonly used and involves inserting a needle through the pregnant woman's abdomen to obtain a sample of amniotic fluid. Amniocentesis is usually performed in the second trimester at approximately 16 weeks gestation and the laboratory analysis may take two to three weeks. The two advantages of chorionic villus sampling are that it is performed during the first trimester and the results are available in about one week. However, as of 1997, amniocentesis is being performed in the first trimester, but this is still very rare. The risk of miscarriage after amniocentesis is 0.5-1 percent (one to two women out of 200) which is lower than that for chorionic villus sampling (1-3 percent).
A non-invasive alternative is the maternal blood test called triple marker screening or multiple marker screening. A sample of the pregnant woman's blood is analyzed for three different markers: alphafetoprotein (AFP), human chorionic gonadotropin, and unconjugated estriol. The levels of these three markers in the mother's blood can identify unborn babies who are at risk for certain genetic or chromosomal defects. This is a screening test which determines the chance that the fetus has the defect, but it can not diagnose defects. A negative test result does not necessarily mean the unborn baby does not have a birth defect. For instance, this screening test can only predict 60-70 percent of the fetuses with Down syndrome. Pregnant women who have a positive triple marker screen are encouraged to undergo a diagnostic test, such as amniocentesis (by the time an AFP is done, it is too late to perform a CVS).
EXPECTED OUTCOME
You should experience no follow-up discomfort. Test results should be available within 1-2 weeks. CVS can accurately rule out or detect certain genetic abnormalities more than 99 percent of the time. Sometimes the results of the test are inconclusive. A woman with inconclusive CVS results may choose to have amniocentesis later in her pregnancy.
Normal results: No genetic, chromosomal, or biochemical abnormalities were found in the fetal cells. The gender of the fetus will be identified but will be made known to the parents only with their approval. More than 95 percent of women who undergo CVS will find out that their fetus does not have any detectable genetic abnormalities.
Abnormal results: Analysis of the cells from the chorionic villus enables the detection of over 200 diseases and disorders such as Down Syndrome, Tay-Sachs disease, and cystic fibrosis. Gross rearrangements of the chromosomes and chromosome additions or losses are detected.
Your health care provider may perform a follow-up ultrasound to make sure the fetus came through the procedure unharmed.
Q & A
Frequently asked questions:
Q: Does CVS detect the same abnormalities that amniocentesis does?
A: With the exception of neural tube defects such as spina bifida, CVS can rule out or detect the same genetic disorders as amniocentesis.
Q: In what other ways does CVS differ from amniocentesis?
A: CVS results are generally available from a few days to two weeks after the procedure, whereas amniocentesis results generally take two to four weeks.
Q: If a birth defect is detected in my fetus, can it be treated?
A: There are a few conditions that can be treated prenatally; however, the majority of congenital birth defects detected by CVS cannot be reversed. Future research may lead to additional treatments for specific congenital birth defects.
POSSIBLE COMPLICATIONS
In some cases, insufficient villi are obtained and the needle or catheter must be reinserted.
Risk of miscarriage (medical estimates between 1-2 percent).
Excessive bleeding.
Risk of infection.
Rh Isoimmunization.
POST PROCEDURE CARE
GENERAL MEASURES
It is generally recommended that women undergoing chorionic villus sampling have someone drive them home and have no plans for the rest of the day. Women with Rh negative blood must receive a Rho (D) immune globulin injection following the procedure. Women should call their health care provider if they experience excessive bleeding, vaginal discharge, fever, or abdominal pain after the procedure.
Bathe or shower as usual unless recommended otherwise by your health care provider. It has been suggested that bathing can dilate blood vessels and increase blood flow thus should be avoided or prohibited for one week after CVS. However, in doing research about CVS, I have not found any information about CVS and post-care recommendations regarding bathing. You may consider avoiding hot water baths or showers during this time and take warm showers (99 to 101°F) only for a few days or so after having CVS. If you have questions or concerns about post-care activity, ask your health care provider.
MEDICATION
Medication is usually not necessary following this procedure.
ACTIVITY
Women are often advised to rest for a few hours after CVS. Some women experience cramping or spotting (bleeding) for a day or two after the procedure.
Avoid strenuous activity and sexual intercourse for several days following the procedure or as recommended by your health care provider.
DIET
No special diet. However, you should follow a healthy, balanced nutritional program for a healthy immune system and to assist in a rapid recovery from your surgery.
MoonDragon's Nutrition Information, Guidelines, Dietary Recommendations
NOTIFY YOUR MIDWIFE OR HEALTH CARE PROVIDER IF...
You experience any pain or cramping.
You have bleeding or fluid leakage from the vagina.
You have any signs and symptoms of infection: fever, body aches, headache, general ill feeling.
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