Chorionic villus sampling, like amniocentesis, is a test designed to detect genetic abnormalities. Unlike amniocentesis, chorionic villus sampling cannot diagnose open neural tube defects.
Developed during the late 1980s, chorionic villus sampling can determine many genetic fetal problems including Down's syndromeA congenital abnormality in which the baby is born mentally retarded, with an average IQ of 50 - 60 and with physical deformation of the face (low set ears, sloping forehead, mongoloid eyes), and shortness of stature.
Downs syndrome is caused by an extra chromosome 21 present in the G group. In a small percentage of cases it can be caused by the switching of chromosomes 14 or15 in the D group or chromosome 21 or 22.
Down's syndrome occurs in about 1 in 650 births, and is more commonly associated with children of mother's over the age of 35. Incidence in children of mothers over the age of 40 can be as high as 1 in 80.
Down's syndrome can be detected prenatally through amniocentesis. The mortality rate is high within the first few years. Down's syndrome is also known as mongolizm, trisomy 21 or trisomy G syndrome.
Visit our comprehensive glossary for more pregnancy terms and definitions. and Tay-Sachs diseaseAn inherited disorder of the nervous system caused by a deficiency of the hexosaminidase A enzyme. The recessive trait occurs predominantly in families of Ashkenazi Jewish origin.
Symptoms first appear in a baby at about 6 months of age after which no new skills are learned. Existing skill are progressively lost. The optic nerve atrophies after about 1 year along and additional symptoms include convulsions and blindness. Death often occurs between 2 and 4 years of age.
There is unfortunately no known therapy, and intervention remains symptomatic and supportive. It can be diagnosed in utero through amniocentesis. Also called amauroticfamilial idiocy, ganliosidosis type I and infantile cerebral sphingolipidosis.
Visit our comprehensive glossary for more pregnancy terms and definitions.. It can determine hemoglobinA complex protein-iron compound which forms part of the red blood cells. Hemoglobin carry oxygen to the cells and return carbon dioxide to the lungs.
Concentration of hemoglobin is different for men and women, with levels of 14 - 18 g/dl and 12 - 16 g/dl respectively. It has a structure which consists of 2 chains one with 141 amino acids and the other with 146. Any alteration in the the chains of just one amino acid alters the hemoglobin properties and is associated with sickle cell anemia.
Visit our comprehensive glossary for more pregnancy terms and definitions. abnormalities such as sickle-cell diseaseA severe, chronic and incurable anemic condition that results from abnormal hemoglobin distorting the red blood cells.
Patients suffer from joint pain, thrombosis, lethargy weakness and fever as well as chronic anemia.
Visit our comprehensive glossary for more pregnancy terms and definitions. and thalassemiaA gentically transmitted hemolytic anemia caused by deficient hemoglobic synthesis that primarily affects people of Mediterranean origin.
Of the two forms, thalassemia major is evident in infancy and is characterized by anemia, fever and failure to thrive. Confirmation involved microscopic examination of the red blood cells.
Red blood cells are destroyed leaving large amounts of iron to be deposited in the skin. Iron is also deposited in the heart, liver and pancreas which may become fibrotic. Frequent blood transfusions are necessary to maintain the bloods ability to transport oxygen. There is currently no cure.
Visit our comprehensive glossary for more pregnancy terms and definitions., or single gene disorders such as cystic fibrosis, hemophilia, Huntington's chorea and muscular dystrophy.
The advantage offered by chorionic villus sampling is an earlier diagnosis of a problem. Chorionic villus sampling provides parents with the safer option of a first trimester abortion should they choose to terminate the pregnancy. The disadvantage of chorionic villus sampling is more risk than amniocentesis, and the inability to detect open neural tube defectsAny of a group of congenital malformations that involve the skull and the spinal column. Most commonly it involves the failure of the neural tube to close properly during embryonic development.
High levels of alphafetoprotein in the amniotic fluid can reveal potential problems prenatally, and the fetus can be scanned using ultrasound. Immediate surgical repair is required.
Visit our comprehensive glossary for more pregnancy terms and definitions..
For a long time doctors have known that the placental tissue, consisting of small subunits called chorionic villi, is made up of the same tissue type as the baby. Undertanding that this living tissue did not need to be cultured like the fetal cells found in the amniotic fluidThe liquid, which is produced by both the fetal membranes and the fetus that surrounds the baby during pregnancy. The liter of fluid at term serves to protect the fetus during pregnancy and also provide active chemical exchange.
The amniotic fluid consists of maternal and fetal plasma in varying concentrations. The pH of the fluid is almost neutral and clear, although lipids and desquamated fetal cells can make it cloudy.
Visit our comprehensive glossary for more pregnancy terms and definitions., they realized that a laboratory could analyze the results in a matter of hours or days instead of the weeks associated with amniocentesis.
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By the late 1980s a procedure was developed to extract a sample of the chorionic villi from the uterus. Two methods are used. The trans-abdominal route is performed very much like amniocentesis. Using ultrasound to locate position, the abdomen is cleaned and numbed with local anesthetic and a long hollow needle is inserted through the abdomen into the uterus. A sample is withdrawn and sent to the laboratory for analysis.
Another method called the trans-cervical route is also employed. After examination of the cervix with a speculum, a small plastic or metal catheter is introduced through the outside edge of the placentaThe placenta is a large disk shaped membrane responsible for providing nourishment to the fetus during pregnancy. It consists of three parts, the fetal part made up from the chorion membrane surrounding the fetus, the maternal part, formed from the decidua basalis layer of the uterine lining, and the intervillous space between the two plates. It is connected to the fetus by the umbilical cord and consists of tissue from both the mother and the embryo.
Its function is complex. It has been described as a simple organ that combines the functions of a kidney-dialysis machine, heart and lung machine and intravenous drip. It consists of enormous numbers of blood vessel branches that permit the exchange of nutrition and oxygen, from the mother's bloodstream to the fetus and the removal of wastes to the mother to be excreted. The placenta's remarkable quality is that it does so without the blood of the mother mixing with that of the baby.
It also is responsible for the production of vital hormones including, estrogen, progesterone, and human chorionic gonadotropin. After birth, the placenta is delivered, and is sometimes referred to as the afterbirth.
Visit our comprehensive glossary for more pregnancy terms and definitions.. A small sample of chorionic villi tissue is removed and analyzed.
Chorionic villus sampling can be performed very early in pregnancy, before the alphafetoprotein test is available. This means that the test is reserved only for mothers who are at high risk of a fetal abnormality. Maternal age is a risk factor for Down's syndrome and mother's who will deliver after their 35th birthday are considered high risk.
Other risk factors are identified through screening and genetic counselling. Carriers of Tay-Sachs disease will be tested. HemoglobinA complex protein-iron compound which forms part of the red blood cells. Hemoglobin carry oxygen to the cells and return carbon dioxide to the lungs.
Concentration of hemoglobin is different for men and women, with levels of 14 - 18 g/dl and 12 - 16 g/dl respectively. It has a structure which consists of 2 chains one with 141 amino acids and the other with 146. Any alteration in the the chains of just one amino acid alters the hemoglobin properties and is associated with sickle cell anemia.
Visit our comprehensive glossary for more pregnancy terms and definitions. abnormalities such as sickle-cell anemiaA severe, chronic and incurable anemic condition that results from abnormal hemoglobin distorting the red blood cells.
Patients suffer from joint pain, thrombosis, lethargy weakness and fever as well as chronic anemia.
Visit our comprehensive glossary for more pregnancy terms and definitions. and thalassemiaA gentically transmitted hemolytic anemia caused by deficient hemoglobic synthesis that primarily affects people of Mediterranean origin.
Of the two forms, thalassemia major is evident in infancy and is characterized by anemia, fever and failure to thrive. Confirmation involved microscopic examination of the red blood cells.
Red blood cells are destroyed leaving large amounts of iron to be deposited in the skin. Iron is also deposited in the heart, liver and pancreas which may become fibrotic. Frequent blood transfusions are necessary to maintain the bloods ability to transport oxygen. There is currently no cure.
Visit our comprehensive glossary for more pregnancy terms and definitions. can be confirmed with chorionic villus sampling. While fortunately rare, for families that are afflicted with inborn errors of metabolism, an enzymeA protein produced by the body's cells which catalyzes chemical reactions in organic matter. While most enzymes catalyze reactions within cells, digestive enzymes, which are produced in much larger quantities, act outside of cells within the digestive tract.
Visit our comprehensive glossary for more pregnancy terms and definitions. deficiency, the incidence is as high as twenty-five percent (1 in 4). Other screening include genetically-linked sex-related diseases such as hemophilia. The incidence of hemophilia in male children of a carrier is as high as fifty percent (1 in 2).
All pregnancies are different and your doctor will advise you if you need chorionic villus sampling. For parents who are in a high-risk group for a chromosomal problem, chorionic villus sampling is able to detect it very early and provides them with the option of a first trimester abortion.
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Chorionic villus sampling increases the risk of miscarriage. The incidence of miscarriage ranges from one to four percent (1 - 4 in 100) higher than the first trimester spontaneous miscarriage rate depending on which study's findings you accept. Because chorionic villus sampling is performed when miscarriage rates are at their peak, it is difficult to determine an exact figure. The truth is probably somewhere between those figures and everyone will admit that the operator's level of skill is the biggest factor in the test's safety. Both the trans-abdominal and the trans-cervical routes are about the same in terms of risk and when choosing a technique, select the one in which the operator has most experience. Ensure that the facility where you have the test done is one with extensive experience in chorionic villus sampling.
In addition to miscarriage there is a suggestion that chorionic villus sampling is responsible for an increased incidence of infection and bleeding. In the mid-1990s, the Centers for Disease Control in Atlanta, reported an increase in limb defects following chorionic villus sampling six times higher than for amniocentesis or no prenatal tests.
In some ways though, chorionic villus sampling is capable of reducing your risks. Terminating a pregnancy during the first trimester is much safer than later in pregnancy. In some ways it is less demanding emotionally than amniocentesis, since you will not yet have felt the first movements of the baby, and the results are received more quickly. You should carefully weigh and discuss the risks with your doctor. Ultimately the decision will depend on the choices you feel comfortable making.
Chorionic villus sampling is usually performed after week nine of pregnancy. Trans-cervical CVS may be performed up to week eleven, and trans-abdominal until week thirteen of pregnancy. After week thirteen amniocentesis, a test which is capable of detecting more problems, becomes available.
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The chorionic villus sampling test is subject to rigorous checks and double-checks as a result of concerns over the accuracy of the test when it was first performed. Initial results from the chorionic villus sampling test may be available within 24 - 48 hours. Full results are usually available in about a week, although a complex analysis, and strict safeguards may mean a two week wait.
The wait is still shorter than that required for amniocentesis, since cell culturing is not required. And since the test is performed earlier you will probably have your results by week twelve or week thirteen instead of week nineteen or week twenty.
A maternal serum alphafetoprotein test will be offered between week fifteen and week sixteen, following the administration of a chorionic villus sampling test.
A normal chorionic villus sampling test result reveals chromosomesOne of the structures within the nucleus of a cell that transmits genetic information. Each of the chromosomes contains a double strand of the helical nucleoprotein deoxyribonucleic acid (DNA). Chromosomes occur in 23 pairs in every human cell.
Visit our comprehensive glossary for more pregnancy terms and definitions. that are normal in size, shape and number. Rarely, chromosome variants or a combination of cell types make it difficult to interpret the results. You and your partner may be required to provide a blood sample to confirm the presence of a problem. Unless specifically requested the results of chorionic villus sampling will not include information about single gene defects or the presence or absence of physical abnormality.
After the results of your chorionic villus sampling test have been received an alphafetoprotein test and ultrasound may be offered to confirm the diagnosis. Depending on the stage of your pregnancy when the chorionic villus sampling test was performed and the results of the test an amniocentesis may be suggested. If you plan to terminate the pregnancy you will need both medical advice and emotional support from your family. No matter how strong your convictions, this is always a difficult and stressful decision to make. Counselling for both parents is recommended, and membership of a support group may prove beneficial.
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