What is amniocentesis?
Now that you have become pregnant, your primary concern is probably your baby’s health. Many of your child’s characteristics are determined at conception. You and the father each donate 23 chromosomes which form the genetic blueprint for your child. So, just as hair and eye color run in families, so can more harmful conditions. The fetal cells, chemicals, and microorganisms surrounding the fetus provide a wide range of information regarding your child’s genetic makeup. Amniocentesis involves extracting and examining these things in order to determine if your baby has a chromosomal disorder of for fetal lung maturity.
Why would I have an amniocentesis?
Amniocentesis can be recommended to you in many different circumstances. These include:
- If you are over 35 years of age. This is done mainly to determine if the fetus has Down syndrome, which is more prevalent among children with older mothers.
- If you have had another child or a close relative that has had a neural tube defect in the past, your doctor may recommend an amniocentesis to rule out the possibility of a defect in your child.
- If both you and the father are carriers for an autosomal recessive inherited disorder such as Tay-Sachs or sickle-cell anemia, an amniocentesis may be recommended to see if your child is suffering from the disorder.
- If you have had a child already that was born with a chromosomal abnormality such as Down syndrome, an amniocentesis will be able to determine if your fetus exhibits the same chromosomal abnormality.
- If you are a carrier for an X-linked (or sex-linked) genetic disorder, an amniocentesis can identify whether the baby has inherited the gene from you and determine the gender in order to see if they will be affected by the presence of the genetic defect.
- If you or the father has an autosomal dominant disorder such as Huntington’s chorea, an amniocentesis will be able to identify if your child will be affected by the disease.
- If any type of infection of the fetus or the mother is suspected an amniocentesis may be recommended.
- If it is necessary to evaluate the maturity of the lungs of the fetus late in the pregnancy, an amniocentesis may be recommended.
Amniocentesis is best performed at 15 to 17 weeks of gestation, but occasionally as early as the 14th or as late as the 20th week. Amniocentesis can also be performed in the last trimester to assess the maturity of the fetal lungs. Test results are usually back in one week.
The expectant mother is positioned on her back with her abdomen exposed. Using, ultrasound, the location of the fetus and placenta are located. This is in order to reduce the chance of accidentally pricking the fetus. The abdomen is then swabbed with antiseptic solution and sometimes a local anesthetic. A long, hollow needle is then inserted through the abdomen and into the uterus. A small amount of amniotic fluid is then withdrawn. Before, during and after the procedure, the mother’s vital signs and fetus’ heart tones are monitored to ensure no complications are experienced. You may also have the option of learning the baby’s gender with the test results, or you may choose to find out the old-fashioned way. From start to finish, the entire procedure should not take more than 30 minutes.
If a genetic disorder is detected, you will be referred to a genetic counselor for further counseling and decision making. The genetic counselor can answer all your questions, and suggest further tests to help see how your child’s health may be affected. In many cases, a genetic counselor can reassure you that the risk to your baby is lower than you feared.
Risks and benefits of amniocentesis
Amniocentesis gives us the ability to extract and examine the fluid from the amniotic cavity. It is more than 99 percent accurate in diagnosis or ruling out Down syndrome, among other things. It rarely results in any symptoms in the mother. It is probably best that you take the remainder of the day off and rest. You may experience a few minutes to a few hours of mild pain or cramping after the procedure. You may also experience some light vaginal bleeding or amniotic fluid leakage. In rare occasions you may experience infection as a result of the procedure or even more severe complications that may lead to miscarriage. It is suggested that it may raise the risk of fetal loss by 0.5%. Thus, amniocenteisis shold only be used when the benefits outweigh the risks.
Revision date: June 18, 2011
Last revised: by Janet A. Staessen, MD, PhD