Chorionic villus sampling (CVS) is a test done early in a person's pregnancy, usually between 10 to 14 weeks gestational age. CVS checks for genetic problems in your baby. During CVS, your doctor takes a small sample of tissue from the placenta for testing. The placenta is an organ that grows in the uterus during pregnancy. This tissue has the same genetic material as your baby. It can show if your baby is developing problems as it grows.

People who have a higher risk or a family history of genetic problems may want to consider CVS testing. Your doctor may advise CVS if:

• You are age 35 or older.
• You have a family history of a genetic disorder, such as Down syndrome, Tay Sachs disease, or cystic fibrosis.
• You and the baby's other parent are carriers for genetic disorders.
• Blood tests or ultrasounds during pregnancy show that your unborn baby is at increased risk of having a genetic condition.

The results of CVS are often available earlier in pregnancy, compared with some other genetic tests, such as amniocentesis. Amniocentesis uses a needle to get samples of amniotic fluid. But CVS is not as accurate as amniocentesis. Other first trimester screening tests provide similar information to CVS, and may be used instead of CVS.

Talk about the risks and benefits of CVS with your doctor. The risks of CVS include:

• Miscarriage
• Infection from the procedure, or passed from you to the baby

Another risk is fetal blood mixing with the birth parent's blood. This may result in the birth parent's immune system destroying fetal blood. This problem is called Rh factor incompatibility. Pregnant people are given a medicine called Rh immunoglobulin after the procedure to prevent this from happening.

Some people may not be able to have CVS. For example, if you have an active vaginal infection, such as herpes or gonorrhea.

CVS is usually done during the first trimester, after 10 weeks of pregnancy. Your doctor will give you instructions. You will likely need a full bladder for the test. Drink plenty of water and don't urinate before the test. You will also have an ultrasound before the test. This is a procedure that uses sound waves and a computer to make images on a screen.

The test can be done through your belly (transabdominal). Or it may be done through your cervix (transcervical). It is common to feel some cramping during and after the CVS procedure.

• The doctor moves a small tube (catheter) through your vagina and cervix to the uterus.
• The doctor uses ultrasound to guide the catheter into place near the placenta.
• The doctor takes a tissue sample using a tiny syringe at the end of the catheter.

• The doctor puts a needle through your belly (abdomen) and into the uterus.
• The doctor uses ultrasound to guide the needle into place near the placenta.
• The doctor takes a small amount of tissue with the syringe.

People who are pregnant with several babies may need to have tissue taken from each placenta. But CVS is not always successful in a person with more than one baby. This is because the position of the babies in the uterus can make it hard to get a tissue sample.

The tissue samples are sent to a lab to be checked. Early results may be available in 48 hours. Final results are often ready in about 7 to 10 days.

After the procedure, call your doctor if:

• You have bleeding
• You have fluid leaking from your vagina
• You have cramps that are getting worse
• You have a fever of 100.4°F (38°C) or higher, or as directed by your doctor

Before you agree to the test or procedure make sure you know:

• The name of the test or procedure
• The reason you are having the test or procedure
• What results to expect and what they mean
• The risks and benefits of the test or procedure
• What the possible side effects or complications are
• When and where you are to have the test or procedure
• Who will do the test or procedure and what that person's qualifications are
• What would happen if you did not have the test or procedure
• Any alternative tests or procedures to think about
• When and how you will get the results
• Who to call after the test or procedure if you have questions or problems
• How much you will have to pay for the test or procedure