Patient education: Amniocentesis (The Basics)

What is amniocentesis? — Amniocentesis is a procedure that takes a small amount of amniotic fluid out of a pregnant person's belly. Amniotic fluid is the liquid that surrounds the fetus, or developing baby, inside the uterus (figure 1).

Why is amniocentesis done? — Amniocentesis is done to get a sample of amniotic fluid. The amniotic fluid is tested to learn about the health of the fetus.

Amniotic fluid is usually tested to find out if the fetus has a genetic problem, like Down syndrome or cystic fibrosis. This might be done if another test, like an ultrasound of the fetus or blood tests on 1 or both parents, showed that the fetus might have a genetic problem.

Sometimes, amniocentesis is done to see if the fetus has an infection.

When is amniocentesis done? — The test is typically done around 16 weeks of pregnancy. The timing depends on why the amniotic fluid is being tested.

How is amniocentesis done? — These are the main steps:

●A doctor or another person called a "sonographer" will do an ultrasound. This lets them see moving pictures of the fetus and the amniotic fluid in your uterus on a screen.

●The doctor will watch the screen as they insert a needle into your belly and then into the amniotic fluid (figure 2).

●The doctor will use the needle and a syringe to take out a small amount of fluid. The test usually takes about 1 to 2 tablespoons of fluid.

●The fluid will be sent to a lab for testing.

Does amniocentesis have any risks? — Yes. Problems are rare, but they can happen. Risks include:

●Amniotic fluid leaking through your vagina – This might stop by itself. If it doesn't, it can cause problems for the fetus, such as infection.

●Infection in the uterus – Infection can lead to pregnancy loss early in pregnancy, or preterm labor and preterm birth later in pregnancy. (Preterm birth is when a baby is born before 37 weeks of pregnancy.)

●The needle can touch the fetus, which in rare cases, can cause an injury.

●Blood from the placenta can leak into your own bloodstream. (The placenta is the organ that brings the fetus nutrients and oxygen and carries away waste.) This can cause problems for later pregnancies.

What happens after amniocentesis? — After amniocentesis, it is normal to have mild cramps in your belly for a short time. Some people also have a small amount of bleeding or "spotting" from the vagina for a short time. You can rest if you want to, but you don't need to avoid physical activity, and can go back to your normal routine right away.

Call your doctor if:

●You continue to have bleeding, or are leaking fluid from your vagina.

●You have cramps that are getting worse.

●You have a fever higher than 100.4°F (38°C).

What if the test shows that my fetus has a genetic problem? — You can talk to your doctor and a genetic counselor before and after the test. They can help you understand the genetic problem, talk to you about your options, and help you decide what to do next.

More on this topic

Patient education: Chorionic villus sampling (The Basics)
Patient education: Cervical insufficiency (The Basics)

Patient education: Amniocentesis (Beyond the Basics)
Patient education: Chorionic villus sampling (Beyond the Basics)