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Harvard Medical School
The risk of miscarriage and other complications from CVS is slightly higher than the risk from amniocentesis, although some parents feel that it is worth the extra risk to be able to make decisions earlier in the pregnancy if the results show the baby has a health problem. There have also been some reports that suggest there is a very small risk of birth defects (abnormal limbs) in the fetus.
One particular difficulty with this test is that due to variability in the cells of the placenta (called mosaicism); occasionally you can have an abnormal test result even if the baby is normal and healthy. This might lead you to make decisions about pregnancy termination that you would not have made if you had better information.
Some women have vaginal bleeding after the procedure. Infection is uncommon.