Amniocentesis

What is amniocentesis?

Amniocentesis is a test performed during pregnancy to diagnose genetic disorders, chromosomal abnormalities, and birth defects. It can also help your doctor diagnose certain infections and the maturity of your baby’s lungs. Amniocentesis involves inserting a needle through the abdomen to take out a small amount of amniotic fluid from inside the uterus. Amniotic fluid is the liquid that surrounds the growing fetus. The amniotic fluid sample is tested in a laboratory.

Amniocentesis is only one method used to screen for fetal abnormalities. You should discuss different screening options with your doctor to understand which option is right for you.

Why is amniocentesis performed?

In rare cases, your doctor may perform amniocentesis to drain extra amniotic fluid from the uterus if there is too much. Too much amniotic fluid (polyhydramnios) can increase the risk of premature labor and delivery and other serious pregnancy complications.

Most commonly, your doctor may recommend an amniocentesis to diagnose certain diseases and conditions of a fetus including:

• Anencephaly, a serious birth defect in which a large part of the brain and skull are not formed
• Cystic fibrosis, a genetic disease in which the body makes too much mucus and sweat
• Down syndrome and other conditions caused by chromosomal abnormalities
• Infections of the uterus or the baby
• Poor lung development. Your doctor may perform an amniocentesis when considering inducing early labor to protect the health of the mother or baby. Looking at the amniotic fluid helps determine if the baby’s lungs are developed enough for birth.
• Rh incompatibility of the mother and baby. This is a condition in which the mother has Rh-negative blood and her baby has Rh-positive blood. This can cause a reaction that breaks down the infant’s red blood cells. The reaction can be mild to serious and cause yellow skin and eyes (jaundice), lethargy, and low muscle tone.
• Spina bifida and other serious neural tube defects caused by incomplete closure of the spine during fetal development

How is amniocentesis performed?

An obstetrician-gynecologist (ob-gyn) or a perinatologist will lead a team to perform your amniocentesis in a doctor’s office or outpatient hospital clinic. An obstetrician-gynecologist is a doctor who specializes in women’s health and pregnancy. A perinatologist, also called a maternal fetal medicine specialist, is a doctor who specializes in high-risk pregnancies. Amniocentesis is most often performed between 15 and 20 weeks of pregnancy (during the second trimester) but can be performed later to test for infection and your baby’s lung development.

The procedure takes about one hour and generally includes these steps:

1. You will dress in a patient gown from the waist up.
2. You will lie on your back on a procedure table. Your doctor may move or tilt the table during your exam.
3. Your doctor will put ultrasound gel on your abdomen. The gel helps the ultrasound equipment make full contact with your skin by eliminating air. It also allows the equipment to slide easily across your skin without discomfort.
4. Your doctor will place an ultrasound transducer on your skin. The transducer is a handheld wand that sends and receives sound waves. The doctor presses it firmly onto your skin and moves it around to see your uterus and fetus. The transducer and sound waves are painless.
5. Your doctor will use the ultrasound images to guide needle insertion. Your doctor will push the needle through the skin of your abdomen until it enters the uterus. He or she then removes about an ounce of amniotic fluid and withdraws the needle.
6. After fluid withdrawal, your doctor may perform more ultrasound imaging to look at how the fetus is developing.
7. Once the ultrasound exam is complete, your doctor will wipe off the gel. The gel is water-based and washes away easily.
8. You may wait a short period while your doctor verifies that the ultrasound imaging is complete. Usually, you can go home immediately after the exam.
9. A laboratory tests your amniotic fluid. The results are typically available in one to two weeks.