From the analysis, the gender of the fetus is determined, as well as potential birth defects, such as Down's Syndrome, where an extra chromosome is present. Analysis will also determine if gross structure of the chromosomes is intact. The simultaneous use of ultrasound has markedly improved the safety of the procedure and lowered the failure rate close to zero. However, available data indicates that there will be one extra miscarriage for every 200 amniocenteses that are done. Although the risks associated with amniocentesis are small the procedure is invasive and therefore only recommended if there is a specific indication.
Most women note that the procedure is about as uncomfortable as having blood drawn from their arm.
After the procedure, decreased activity is suggested for about 24 hours. One to two percent of women will experience spotting or some loss of amniotic fluid vaginally. Most CVS procedures are done transcervically, and ultrasound is used to guide the needle through the cervix and into the chorionic plate of the developing placenta. Because a larger number of cells are obtained with CVS, fetal karyotype results are often availablein 2-3 days. CVS may also be performed abdominally, similar to the technique for amniocentesis.