Chorionic villus sampling (CVS) refers to a procedure for the prenatal diagnosis of genetic disorders in which small samples of the placenta are obtained for chromosome or DNA analysis. It is generally performed during the first trimester (after 10 weeks), thus reducing the at-risk couple's period of anxious waiting for test results and permitting access to pregnancy termination at a safer and more discreet time. A larger amount of DNA is derived from CVS than from cells obtained at amniocentesis, thereby allowing reliable DNA analysis within hours or days of sampling. (See "Diagnostic amniocentesis".)
Introduction of first trimester screening programs has led to a decrease in the utilization of CVS, particularly among women 35 years or older [1-3]. (See "First trimester combined test and integrated tests for screening for Down syndrome and trisomy 18" and "Prenatal diagnosis using cell-free nucleic acids in maternal blood".)
CVS is performed as an ambulatory procedure, without analgesia or local anesthesia . A transvaginal sonographic examination should precede the procedure to determine the number of embryos and chorionicity, document fetal viability, and detect major fetal structural anomalies.
Personnel — The sonographer and the physician performing the CVS should be coordinated with one another. Coordination comes from experience; a learning curve for safe and successful performance of the procedure has been described . An assistant trained in the sonographic appearance of a transcervical catheter or transabdominal needle is also essential to ensure smooth performance. A second trained assistant with an on-site microscope can provide rapid evaluation of sample adequacy, assess the quality of the specimen obtained, and select the chorionic villi.
Technique — Two approaches are available for obtaining chorionic tissue: transcervical (TC) and transabdominal (TA).