Amniocentesis is a diagnostic test in which a small amount of the amniotic fluid surrounding the fetus is removed for testing. It is usually recommended following an abnormal triple test result. It is done to look for birth defects and genetic problems in the developing fetus.
Why is an amniocentesis performed ?
It is done to check for birth defects such as chromosomal abnormalities and Down’s syndrome.
Amniocentesis is recommended for women with significant risk of genetic disease. These women include those who :
- are 35 years or older at the time of pregnancy
- have a child or pregnancy with birth defect
- have an abnormal ultrasound
- have a family history of birth defects
Even though this test may not detect all birth defects, it is used to check for the following disorders if mother carries a significant risk :
- Down syndrome
- Muscular dystrophy
- Cystic fibrosis
- Sickle-cell disease
It can also detect neural tube defects such as spina bifida and anencephaly. The ultrasound done during an amniocentesis may also detect birth defects such as cleft palate, cleft lip, club foot, or heart defects.
During an amniocentesis, you can ask for your baby’s sex. It is the most accurate way to find out your baby’s gender.
It may be done to check the severity of fetal anemia in babies with Rh disease and if the fetus needs a lifesaving blood transfusion.
When done in the third trimester, this test can also be used to check for infections of the amniotic fluid or evaluate the maturity of the baby’s lungs before delivery.
This test also provides access to DNA for paternity testing prior to delivery.
How to prepare for the test ?
You must have a full bladder for the test. Your blood type and Rh factor may be checked before the test. If you are RH negative, you may get a shot of medicine called RhoGAM .
How is an amniocentesis performed ?
An ultrasound is used to determine the safe place where the needle can enter the amniotic sac so that the fluid can be safely removed. A sample of the amniotic fluid is collected through the needle which is then sent to the lab for analysis. This procedure may take about 45 minutes even though it takes less than 5 minutes to collect the fluid. The results may take anywhere from a few days to a couple of weeks.
When is an amniocentesis performed ?
This test is usually performed between 14 and 20 weeks even though in some health facilities, it may be performed as early as 11 weeks.
It may also be done in the third trimester when membranes rapture prematurely to check for uterine infections.
What do the results mean ?
A normal result means that no chromosomal of genetic problems were found in your baby. It also means that Bilirubin and alpha fetoprotein levels appear normal .
NOTE : Even with a normal results , there may still be some other birth defects in the baby.
An abnormal result means your baby has a gene or chromosomal defect. It also means he may have a birth defect such as spina bifida.
Does an amniocentesis carry any risk ?
A miscarriage is a major risk although this is extremely rare. Other risks include :
- fluid leakage
- minor leakage at the punctured site
Amniocentesis. National library of Medicine. MedlinePlus. http://www.nlm.nih.gov/medlineplus/ency/article/003921.htm Accessed October 22, 2014
Pregnancy and amniocentesis. WebMD. http://www.webmd.com/baby/guide/amniocentesis. Accessed October 22, 2014