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Amniocentesis is a procedure in which you doctor removes a small amount of amniotic fluid from your womb. The amount of fluid removed is about 30 cubic centimeters. Amniotic fluid surrounds your unborn baby. This fluid contains some of your baby’s cells and is used to find out if your baby has any genetic abnormalities. It’s also used to determine if your baby’s lungs are mature enough to survive outside the womb.
Your doctor will use a long, thin needle to collect a small amount of amniotic fluid. This fluid surrounds and protects the baby while they’re in your womb. A laboratory technician will then test the fluid for certain genetic disorders, including Down syndrome, spina bifida, and cystic fibrosis.
The test results can help you determine whether to continue with your pregnancy. The test can also tell you whether or not your baby is mature enough to be born. It’s also helpful for determining whether you need to deliver early to prevent complications from your pregnancy.
Abnormal prenatal screening test results are one common reason you might need amniocentesis. Amniocentesis can help your doctor confirm or deny any indications of abnormalities found during the screening test. If you’ve already had a child with a birth defect or a serious abnormality of the brain or spinal cord called a neural tube defect, amniocentesis can check whether your unborn child also has the condition.
If you’re 35 years or older, your baby is at a higher risk for chromosomal abnormalities, such as Down syndrome. Amniocentesis can identify these abnormalities. If you or your partner is a known carrier of a genetic disorder, such as cystic fibrosis, amniocentesis can detect whether your unborn child has this disorder.
Complications during pregnancy will sometimes require you to deliver your baby earlier than the full term. Maturity amniocentesis can help determine if your baby’s lungs are mature enough to allow your child to survive outside of the womb.
You may also need an amniocentesis if your doctor suspects that your unborn child has an infection or anemia. Your doctor may also order amniocentesis if they think that you have a uterine infection. If it’s necessary, the procedure can also be done to decrease the amount of amniotic fluid in your womb.
This test is an outpatient procedure, so you won’t need to stay in the hospital. Your doctor will first perform an ultrasound to determine the exact location of your baby in your uterus. An ultrasound is a noninvasive procedure that uses high-frequency sound waves to create an image of your unborn baby. Your bladder must be full during the ultrasound, so drink plenty of fluids beforehand.
After the ultrasound, your doctor may apply numbing medication to an area of your belly. The ultrasound results will give them a safe location to insert the needle. Then, they’ll insert a needle through your belly and into your womb, withdrawing a small amount of amniotic fluid. This portion of the procedure usually takes about two minutes.
The results of genetic tests on your amniotic fluid are usually available within a few days. The results of tests to determine the maturity of your baby’s lungs are usually available within a few hours.
Amniocentesis usually occurs between 16 to 20 weeks, which is during your second trimester. Complications associated with amniocentesis include the following:
In rare cases, this test may cause some of your baby’s blood cells to enter your bloodstream. This is important because there’s a type of protein called the Rh factor. If you have this protein, your blood is Rh-positive. If you don’t have this protein, your blood is Rh-negative. It’s possible for you and your baby to have different Rh classifications. If this is the case and your blood mixes with your baby’s blood, your body may react as if it were allergic to your baby’s blood. If this happens, your doctor will give you a drug called RhoGAM. This medication will prevent your body from making antibodies that will attack your baby’s blood cells.
If the results of your amniocentesis are normal, your baby most likely doesn’t have genetic or chromosomal abnormalities. In the case of maturity amniocentesis, normal test results will assure you that your baby is ready to be born with a high likelihood for survival.
Abnormal results may mean that your baby has a genetic problem or serious birth defect. Discuss all test results with your doctor and your partner so that you can make an informed decision about whether or not to continue your pregnancy. This is a difficult time for parents, so seek support from your loved ones, your doctor, or a support group.
Written by: Heather Ross
Medically reviewed on: Jan 11, 2016: Steven Kim, MD
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