Possible reasons for having a CVS can include:
CVS is similar to amniocentesis in terms of fetal mortality (0.2 to 0.3%). Apart from a risk of miscarriage, there is a risk of infection and amniotic fluid leakage. The resulting amniotic fluid leak can develop into a condition known as oligohydramnios which is low amniotic fluid level. If the resulting oligohydramnios is not treated and the amniotic fluid continues to leak it can result in the baby developing hypoplastic lungs (underdeveloped lungs).
It is important after having a CVS that the OB/GYN follow the patient closely to ensure the patient does not develop infection.
A small percentage (1-2%) of pregnancies will have confined placental mosaicism, where some but not all of the placental cells tested in the CVS will be abnormal, even though the pregnancy is unaffected. Cells from the mother can be mixed in with the placental cells obtained from the CVS procedure. Occasionally if these maternal cells are not completely separated from the placental sample, this can lead to discrepancies with the results. This phenomenon is called Maternal Cell Contamination (MCC). CVS can not detect all birth defects. Only chromosomal abnormalities are usually tested for, or other specific genetic disorders if there is family history or other reason to test.