Amniocentesis
Amniocentesis is a test sometimes done during pregnancy that looks for birth defects and genetic problems in the developing baby. Amniocentesis removes a small amount of fluid from the sac that surrounds the baby in the womb (uterus). It is usually done in a doctor's office or medical center on an outpatient basis. You will probably have an ultrasound first. This helps the perinatologist find out exactly where the baby is in your womb. A local anesthesia is normally not necessary to perform the procedure. In case of increased anxiety, numbing medicine can rubbed onto part of your belly or can be given through a shot in the skin on the belly area. Then the perinatologist inserts a long, thin needle through your belly and into the womb. A small amount of fluid (about 4 teaspoons) is removed from the sac surrounding the baby.
The fluid is sent to a laboratory, where:
- Genetic studies are done.
- Levels of alpha-fetoprotein are measured.
- Other tests may be done.
Results are usually back within 2 weeks.
No specific preparations for the test are needed. Your Rh factor should be clearly known and documented in your maternity papers. You may get a shot of medicine called RhoGAM if you are Rh negative.
Amniocentesis is most often offered to women at increased risk for bearing a child with birth defects. This includes women who:
- Will be 35 or older when they give birth.
- Had a screening test result that indicates a possible birth defect or other problem.
- Have had babies with birth defects in previous pregnancies.
- Have a family history of genetic disorders
Genetic counseling is an option prior to the procedure. This will allow you to:
- Learn about other prenatal tests
- Make an unhurried, informed decision regarding options for prenatal diagnosis.
This test can also be done to help:
- Determine how well your baby's lungs are developed late in the pregnancy
- Detect a blood type mismatch between the mom and the baby (RH incompatibility))
- Diagnose an infection in the baby
Amniocentesis can be used to diagnose many different gene and chromosome problems in the baby, including:
- Down syndrome
- Rare, metabolic disorders that are passed down through families
It can also help:
- Determine how well the baby's lungs are developed
- Detect spina bifida and other neural tube defects
- Detect Rh incompatibility
- Diagnose an infection in the baby
A normal result means:
- No genetic or chromosome problems at the level a DNA lenght exceeding 10 MB were seen in your baby
- Bilirubin and alpha fetoprotein levels appear normal
Note: Even with normal results after an amniocentesis, your baby may still have other types of birth defects. Therefore, a supplementary anomaly scan at 20 weeks gestation is always recommended.
An abnormal result may mean your baby has:
- A gene or chromosome problem, such as Down syndrome and many others
- Birth defects that involve the spine or brain, such as spina bifida
Talk to your doctor about the meaning of your specific test results.
- How the condition or defect may be treated either during or after the pregnancy
- Special needs your child my have after birth
- What other options you have regarding maintaining your pregnancy
Risks are minimal, but may include:
- Infection or injury to the baby
- Miscarriage
- Leaking of amniotic fluid
- Vaginal bleeding
Further information:
– Practical introduction to amniocentesis
– Video Amniocentesis (Genesys fertility center)