gynecology and obstetrics
Procedures for Prenatal Genetic Diagnosis
Chorionic Villus Sampling
In chorionic villus sampling (CVS), chorionic villi are aspirated into a syringe and cultured. CVS provides the same information about fetal genetic and chromosomal status as Amniocentesis and has similar accuracy. However, CVS is done between 10 weeks gestation and the end of the first trimester and thus provides earlier results. Therefore, if needed, pregnancy may be terminated earlier (and more safely and simply), or if results are normal, parental anxiety may be relieved earlier. Unlike amniocentesis, CVS does not enable clinicians to obtain amniotic fluid, and alpha-fetoprotein cannot be measured. Thus, women who have CVS should be offered maternal screening for serum alpha-fetoprotein at 16 to 18 weeks to assess risk of fetal Maternal serum screening for neural tube defects . Depending on placental location (identified by ultrasonography), CVS can be done by passing a catheter through the cervix or by inserting a needle through the woman’s abdominal wall. After CVS, Rho(D) immune globulin 300 mcg is given to Rh-negative unsensitized women. Errors in diagnosis due to maternal cell contamination are rare. Detection of certain chromosomal abnormalities (eg, tetraploidy) may not reflect true fetal status but rather mosaicism confined to the placenta. Confined placental mosaicism is detected in about 1% of CVS specimens. Consultation with experts familiar with these abnormalities is advised. Rarely, subsequent amniocentesis is required to obtain additional information. Rate of fetal loss due to CVS is similar to that of Amniocentesis (ie, about 0.2%) ( 