Amniocentesis

What is amniocentesis?

Amniocentesis is a procedure that involves the extraction of a small amount of amniotic fluid from the uterus. Usually, about 30cm3 of fluid is extracted. The amniotic fluid is that fluid that surrounds the fetus in the womb. Present in the fluid are some of the fetal cells. Testing this fluid gives a clue as to whether the baby has any genetic abnormalities or not. It also helps the physician to determine whether the baby’s lungs can cope with the external environment.

The amniotic fluid is collected with a thin long needle. This fluid is responsible for the protection of the baby while in the womb. The fluid is tested by the laboratory technician to determine the presence of certain disorders including Spina bifida, cystic fibrosis and Down syndrome.

With the test results, the mother can determine whether or not to continue with the pregnancy. With the test, you will also know whether the baby is mature enough to be born. With the test results, the mother can also determine whether to deliver early to prevent pregnancy-related complications.

Amniocentesis
Photo Credit: Mayo Clinic

Why do women need an amniocentesis?

Abnormal prenatal screening test results are an important reason why one needs to do an amniocentesis. With amniocentesis, a physician can deny or confirm the presence or indication of abnormalities during the screening test. If your previous pregnancy resulted in the birth of a child with a defect, then you can confirm the health status of the unborn fetus via amniocentesis.

If you are above 35 years, your baby is at a high risk of chromosomal abnormalities such as Down syndrome. With amniocentesis, one can check whether or not these abnormalities are present. Also, if your partner carries a genetic disorder, like cystic fibrosis, then you can detect if your child has this abnormality or not, using amniocentesis.

At times, women may experience complications during pregnancy. These complications force one to deliver prematurely. Maturity amniocentesis allows one to determine whether or not the baby’s lungs are mature to handle the external environment. Amniocentesis is also important to check for the presence of anemia or an infection. An amniocentesis may also be done if your physician suspects that you have a uterine infection. In some cases, an amniocentesis may be done just to reduce the quantity of amniotic fluid in your uterus.

The procedure for amniocentesis

Amniocentesis is an outpatient procedure. This implies that the patient will not need to stay in the hospital. The first procedure will be an ultrasound. The aim of this is to detect the exact position of the fetus in the uterus. An ultrasound makes use of sound waves of very high frequency to create an image of the unborn fetus. It is important that the bladder is filled prior to ultrasound, so drink a lot of fluid beforehand.

After the ultrasound procedure, the physician will numb certain parts of your belly. The results gotten from the ultrasound will give the physician a safe location to insert the needle. The needle will then be inserted through your belly, and then to the uterus, withdrawing a small amount of the amniotic fluid. It takes about two minutes to carry out this portion of the procedure. Results of the genetic test on the amniotic fluid are available in a matter of days. Tests to determine the maturity of a baby’s lungs are available in a matter of hours.

Any complications associated with amniocentesis?

The test is done within the second trimester of pregnancy i.e. between 16 to 20 weeks. Complications associated with this test include:

  • A 0.6 percent risk of miscarriage if the procedure is done during the second trimester. The risk is a bit higher if the test is done before 15 weeks of pregnancy.
  • Cramps may occur in some women after the procedure
  • A small amount of bleeding from the vagina may occur after the procedure.
  • In rare cases, the amniotic fluid may leak from the body.
  • Uterine infection is another rare complication
  • If the mother has an infection such as HIV or hepatitis C, then this may be transferred to the baby courtesy of amniocentesis.

In very rare cases, amniocentesis may cause the flow of the baby’s cells into the mother’s bloodstream. This is of clinical importance due to the presence of a protein identified as Rh factor. If this protein is present in the blood, then the mother is Rh positive. If it is absent, then you are Rh negative. It is possible for mother and child to have different Rh classifications. In such cases, if the mother’s and the baby’s blood mixes, then the body may react as if it were allergic to the baby’s blood. A drug known as RhoGAM will be administered if this happens. This medication prevents the formation of antibodies that will attack the baby’s blood cells.

What the amniocentesis test results mean

If the results are normal, then it implies that your baby does not have any chromosomal or genetic abnormality. 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 test results imply that the baby has a serious birth or genetic defect. All test results should be discussed with your physician and your partner so you can both make an informed decision about whether or not to continue with the pregnancy. This is usually a difficult time for both parents, so seek support from your doctor, loved ones or a support group.