Genetic testing – evaluating your baby’s chromosomes or genes for abnormalities – is commonly discussed at an early prenatal visit. If any of the relatives of the baby’s mother or father has genetic disorders like Down syndrome, cystic fibrosis, or sickle cell disease, among others, your healthcare provider or genetic counselor may suggest testing to determine if your baby could be affected as well. Testing options commonly include amniocentesis, chorionic villus sampling (CVS) or cell-free fetal DNA testing.
The decision to undergo genetic testing is a personal choice. To aid your decision-making process, Pregistry is providing a series of articles to provide you with an explanation of what each test is, when and why it might be recommended, and what the results mean.
This blog talks about Amniocentesis.
All about Amniocentesis
Amniotic fluid surrounds your growing baby and is comprised of water, fetal cells and a variety of chemicals produced by the baby. During an amniocentesis, a sample of amniotic fluid is aspirated (withdrawn by a syringe) from the uterus and sent for testing. It is generally offered after 15 weeks of pregnancy, however, in rare instances it can be done as early as 11 weeks.
This form of diagnostic testing is done for a multitude of reasons but most commonly to test for certain genetic abnormalities such as Down syndrome or spina bifida. It can also be done to evaluate fetal lung maturity to determine if the lungs are mature enough for delivery, to check for fetal infection or illness, or to decrease the amount of amniotic fluid within the uterus. An amniocentesis for fetal lung maturity is done between weeks 32 and 39.
Who should and should not have an amniocentesis?
Genetic amniocentesis may be recommended if:
- the results of your first trimester genetic screening blood test were positive or uncertain
- you had a prior pregnancy with a chromosomal or neural tube abnormality
- you are 35 years and older
- you have a family history of genetic abnormalities or you or your partner are known to be a carrier of a gene that may result in an abnormality in your offspring.
Other reasons for considering an amniocentesis include evaluation of fetal infection/illness, to decrease the amount of amniotic fluid in the uterus and/or to evaluate anemia in fetuses with Rh sensitization.
Certain women may be advised against undergoing an amniocentesis, for example those with a partial placental abruption or placenta previa, a history of premature labor, and/or cervical incompetence.
Are there risks associated with amniocentesis?
As with any procedure, an amniocentesis does have certain risks which include:
- Miscarriage: There is a 1 in 300 to 1 in 500 risk for miscarriage when undergoing a second trimester amniocentesis. This risk is higher when amniocentesis is performed prior to 15 weeks gestation.
- Needle Injury: Although serious needle related injuries are rare; they occur when the baby moves a limb that comes in contact with the needle.
- Leaking Amniotic Fluid: At times, amniotic fluid can leak into the vagina following the procedure, however this is a rare occurrence. But if there is chronic leaking, the amount of amniotic fluid cushioning the baby may decrease. This may put pressure on the baby’s growing body and lead to orthopedic complications like club foot or hip dysplasia.
- Rh sensitization: At times, fetal blood cells can leak into the maternal bloodstream. If you are Rh negative and the baby is Rh positive, your blood cells may think your baby’s blood cells are foreign invaders. A medication called Rh immunoglobulin, will be given to you after completion of the procedure. This will prevent your body from producing antibodies that fight against the fetal blood cells. Your healthcare provider may obtain a blood test to determine if you have begun to create antibodies.
- Infection: Although rare, amniocentesis may cause a uterine infection.
- Infection transmission: If you have an infection such as hepatitis C, toxoplasmosis or human immunodeficiency virus (HIV), the procedure increases the risk that your infection will be passed on to the fetus.
What do the results tell me?
Once the results of the amniocentesis are available, your healthcare provider or genetic counselor will discuss the results with you. When undergoing an amniocentesis for lung maturity reasons, the results will let your healthcare provider know if your baby’s lungs are mature enough for him or her to be delivered. When done for genetic reasons, the results will indicate if your baby has a chromosomal abnormality such as Down syndrome or other disorder and your options will be discussed with you.
Speak with your healthcare provider or genetic counselor if you are considering genetic testing and/or if you have additional questions about which test (amniocentesis, chorionic villus sampling, or cell-free fetal DNA testing) is best for you.
