Risks

Chorionic villus sampling carries various risks, including:

• Miscarriage. The risk of miscarriage after chorionic villus sampling is estimated to be 0.22 percent.

• Rh sensitization. Chorionic villus sampling might cause some of the baby's blood cells to enter your bloodstream. If you have Rh negative blood and you haven't developed antibodies to Rh positive blood, you'll be given an injection of a blood product called Rh immune globulin after chorionic villus sampling.

  This will prevent your body from producing Rh antibodies that can cross the placenta and damage the baby's red blood cells. A blood test can detect if you've begun to produce antibodies.

• Infection. Very rarely, chorionic villus sampling might trigger a uterine infection.

Some older studies suggested that chorionic villus sampling might cause defects in a baby's fingers or toes. However, the risk appears to be a concern only if the procedure is done before week 10 of pregnancy.