An amniocentesis test examines the amniotic fluid surrounding the developing baby. The test is not offered to every pregnant woman but it is suitable for certain situations.
What Is an Amniocentesis Test?
An amniocentesis test uses about two tablespoons of amniotic fluid, which contains discarded cells from the fetus, to detect certain types of birth defects and determine the gender. The cells contain chromosomal information that can tell doctors whether the baby is at risk for certain birth defects. The fluid contains substances in addition to cells, which can help detect certain types of birth defects and genetic diseases. The baby's maturity may also be determined by measuring these substances.
In normal development, each cell of the fetus contains 46 chromosomes organized in 23 pairs. Differences in pattern and number can be a sign of certain genetic disorders.
The test is not used to detect many non-chromosonal common birth defects.
The procedure consists of inserting a needle into the pregnant woman's belly to reach the uterus. An obstetrician does the test in an outpatient setting, either the doctor's office or at a hospital. The procedure progresses as follows:
- Patient lies on her back on a table that is raised to help relax the muscles in the belly.
- The lower part of her belly is cleaned.
- The obstetrician uses a fetal ultrasound to check the position of the placenta and the baby.
- A long, thin needle is carefully inserted into the cleansed belly and into the uterus.
- The obstetrician removes about two tablespoons of fluid into a syringe that is attached to the needle.
- The needle is removed and the site of entry is covered with a bandage.
The procedure takes about 15 minutes to complete with the needle being inside the uterus for about one or two minutes. The doctor checks the patient's blood pressure, breathing, and pulse during the entire procedure and after it is completed. The baby's heart rate is monitored throughout the test as well.
After the Test
Women who have an amniocentesis test may feel mild cramps and are advised against doing anything strenuous for several hours after the test is completed. Sex should be avoided during the downtime as well. In most cases, the patient should be able to resume normal daily activities in about 24 hours.
Patients who experience any of the following symptoms should call their doctor immediately:
- Severe or moderate pain
- Severe or moderate cramping
- Swelling or redness where the needle was inserted
- Fluid leaking from the injection site
- Fluid leaking from the vagina
When Is the Test Offered?
An amniocentesis test is offered to pregnant women who are concerned about possible problems with fetal development. The test is administered between week 15 and week 20. Conditions that may make a test a consideration include:
- Problems found in the fetal ultrasound
- Abnormal first trimester birth defect screening tests
- Genetic problems in close relatives
- Abnormal triple or quadruple screening test
- Advanced maternal age
- History of birth defects in either parent's family history
- Either parent is a carrier of an inheritable disease
- History of gender-linked diseases
Third Trimester Testing
In some cases, amniocentesis may be done later during the pregnancy if there are concerns about infection in the amniotic fluid. According to Children's Hospital in Pittsburgh, Pennsylvania, chorioamnionitis is an infection in the amniotic fluid that can lead to a blood infection in the pregnant woman, called bacteremia. Bacteremia may lead to preterm birth and the baby may develop a serious infection as well.Symptoms of chorioamnionitis include:
- Strong, unpleasant odor in the amniotic fluid
- Pain or tenderness in the uterus
- Increased heart rate in the baby and mother
- Chorioamnionitis may also be called amnionitis or intra-amniotic infection
Women at risk for having their babies early may have a test to see if the lungs are developed enough for the babies to breathe independently after delivery. Substances found in the amniotic fluid can determine how far the lungs have developed. The fluid can also help determine what kind of breathing support will be necessary after an early delivery, if any.
When performed by a skilled physician and with careful ultrasound guidance, amniocentesis is usually a safe procedure. But, like any test, it does have some risks.
- Miscarriage. Research puts the risk of miscarriage at less than 1 percent. The earlier the amnio occurs, the higher the risk.
- Needle pokes. If the baby moves unexpectedly during the procedure, it's possible for him to get pricked by the needle. The physician should anticipate this and will be watching very closely so she can remove the needle quickly if needed.
- Cramps. Some mild to moderate cramping in the hours after an amnio is not uncommon. For this reason, it's a good idea to have someone else drive you home after the procedure.
- Bleeding. Similar to a blood draw from your arm, there may be some bleeding at the site where the needle was placed. Some women may also notice a small amount of vaginal bleeding as well following the test.
- Infection. Your doctor will clean the area where the needle is inserted prior to beginning the test and will use only sterile supplies. But, in rare cases, an infection may still occur.
Preparing for Amniocentesis Testing
Preparing for an amniocentesis test requires more than getting ready immediately before the procedure. It is important to consider risks and necessity of the test.
Decisions to make after the test can be challenging as well. WebMD offers a medical test information form that can help patients make a decision about having the procedure done.