Chorionic villus sampling
Chorionic villus sampling (CVS) is a prenatal diagnostic procedure typically performed between the ninth and thirteenth weeks of pregnancy to identify genetic and chromosomal abnormalities in the fetus. It is particularly recommended for expectant mothers who have an increased risk of genetic disorders, such as Down syndrome, cystic fibrosis, and sickle cell disease. The procedure involves collecting a small sample of chorionic villi, which are tiny projections from the placenta that share genetic material with the fetus. This sample can be obtained either through the abdomen or via the cervix, guided by ultrasound for accuracy.
Results from CVS are generally available within one to two weeks, providing early insights that can be crucial for parents considering their options. While CVS offers the advantage of early detection, it also carries potential risks, such as vaginal bleeding, cramping, and a slightly elevated chance of miscarriage compared to other procedures like amniocentesis. Additionally, there are concerns about the accuracy of results, as some abnormalities detected in placental cells may not reflect the fetal condition. Therefore, individuals considering CVS should discuss the procedure's benefits and risks with their healthcare provider to ensure informed decision-making.
Chorionic villus sampling
Anatomy or system affected: Reproductive system, uterus
Definition: The collection of a small sample of chorionic villi tissue from the finger-like projections of the placenta to detect genetic and chromosomal abnormalities through karyotyping
Indications and Procedures
Chorionic villus sampling can be performed between the ninth and thirteenth weeks of pregnancy to detect genetic and chromosomal abnormalities. The procedure is recommended when there is an increased risk of genetic disorders in the fetus, such as Down syndrome, sickle cell disease, cystic fibrosis, and muscular dystrophy.
Chorionic villus sampling involves collecting a small sample of the chorionic villi, the finger-like projections on the developing placenta, which delivers food and oxygen to the fetus. A sample of chorionic villi can be obtained from the point at which the placenta attaches to the uterine wall, either by inserting a needle through the abdomen or by entering the cervix with a small flexible catheter through the vagina. The choice of approach depends on the position of the placenta. An antiseptic cleansing solution is applied to the area prior to sampling, and ultrasound is used to locate the fetus and the placenta and its villi.
A ten- to twenty-five-milligram sample is collected using a syringe, which is then purified and sometimes cultured. Since the chorionic villi originate from the same cell as the fetus, they normally have the same genetics. Results are available within one to two weeks.
Uses and Complications
Along with exposing genetic and chromosomal disorders, chorionic villus sampling can be used to determine the sex of the embryo but should never be used for this purpose alone because of the risks involved. Testing can be done early in the pregnancy. Therefore, should the woman choose to terminate her pregnancy, an easier first-trimester abortion can be performed. If the results from the test are favorable, the parents have early peace of mind.
Possible complications from chorionic villus sampling include vaginal bleeding, cramping, and uterine infection. More serious risks involve Rh incompatibility between maternal and fetal blood, spontaneous abortion (miscarriage), and even possible fetal injury. A 2003 intervention review published in the Cochrane Database of Systematic Review found that the rate of miscarriage was significantly higher with chorionic villus sampling than with amniocentesis, performed after sixteen weeks and yielding the same information. A study published in April 2020 found that the overall risk of miscarriage from chorionic villus sampling remained around 1 percent and was affected more by the background demographics of the patient than the procedure itself.
Some studies suggest that chorionic villus sampling itself may cause some birth defects; others do not. Also, the procedure can be inaccurate. Abnormalities may occur in some placental cells but not in the fetus. This might lead to aborting a healthy fetus. With the guidance of a physician, the risks and benefits should be compared with other available procedures.
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