Chorionic Villus Sampling
Chorionic villus sampling is the oldest of prenatal testing and is applied between 11 and 14 week of pregnancy. In CVS testing, a thin catheter is incorporated in the uterus through the vagina (trans-cervical approach) or through the abdomen (transabdominal route) with ultrasound guidance of the aspirated placental tissues (chorion) for analysis. The chorionic villi are outgrowths of placental tissues which are genetically identical to the fetus, and are developed very early in pregnancy so that their analysis is possible before amniocentesis test. Chorionic villus sampling is a test in the prenatal testing where you take the chorionic villi from the placenta for testing.
During pregnancy, the placenta provides oxygen and nutrients to babies and removes waste products from the blood of a child. It’s function is to protect a child. The chorionic villi are part of the placenta and the largest share in the genetic structure of babies.
CVS testing is excellent for diagnose of inherited metabolic defects – lack or insufficient function of some enzymes. Typical disorders that can be diagnosed by this method are cystic fibrosis, hemophilia, thalassemia and other hemoglobinopathies, Huntington’s chorea and muscular dystrophy. The primary goal of chorionic villus sampling remains the determination of the karyotype and identification of chromosomal abnormalities at a very early stage of pregnancy, so that parents have enough time to prepare emotionally for the birth of the injured child or an abortion.
Although chorionic villus sampling can provide valuable information about the health of your child, your decision to have an invasive diagnostic prenatal testing is serious. It is important to understand the risks of chorionic villus sampling and be ready for results.
CVS testing – Chorionic Villus Sampling
CVS testing is generally recommended if the ultrasound showed a striking finding, or if there is suspicion of a hereditary disease (for example, on the basis of already recorded in the family) that must be clarified as soon as possible. The doctor usually in the abdominal wall introduce a hollow needle, and by it removes a few millimeters of chorionic tissue. The best place for CVS testing is discovered by ultrasound, and the entire chorionic villus sampling is controlled by ultrasound.
Since the chorionic villi have the same genetic pattern, such as fetus, analysis of the chorionic villi can alert you to a number of genetic defects. When the villi are obtained next step is in laboratory: examining of the chromosomal composition of the child. In addition, using DNA analysis can be targeted an observation for a hereditary diseases or muscle metabolism. First results are available after one to eight days.
The rate of abortions is 0.5 percent, slightly higher than the rate of abortion during testing of the amniotic fluid. In very rare cases it can happen for child to come to the world before it’s time, or the consequences of the procedure show very hard for a child so that he later dies during pregnancy. Furthermore, more often than in tests of the amniotic fluid it happens that the amount of the removed tissue is not enough – then the procedure must be repeated.
Similar to amniocentesis, chorionic villus sampling is retrograde because more pregnant women choose an alternative – a combined testing for Down syndrome. More commonly, chorionic villus sampling is performed if the family has hereditary metabolic or muscle diseases, such as muscular dystrophy. Muscular dystrophy with the use chorionic villus sampling can be nicely seen in pregnancy.
Chorionic villus sampling results are more accurate then in amniocentesis test. In about two percent of cases chorion cells differ genetically from the cells of the child. In this case it may be that chorionic villus cells showed chromosomal disorders (eg trisomy 21), but that child has a normal structure of chromosomes. In this case, your doctor may want to check again the result of the chorionic villi, which indicates a disorder of the fetus, before mentioning further measures. Here you lost time, unlike with the amniocentesis. Also, a good advice if this happens is to change doctor and do again CVS testing at some other doctor.