What is chorionic villus sampling?
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 increased risk of genetic disorders in the fetus such as Down syndrome, sickle cell disease, 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 10- to 25-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.
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 is significantly higher with chorionic villus sampling than with amniocentesis, performed after sixteen weeks and yielding the same information.
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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