Amniocentesis Explained
- What Is An Amniocentesis?
- Why Is An Amniocentesis Performed?
- When Is An Amniocentesis Performed?
- How Accurate Is An Amniocentesis?
- What Disorders & Defects Can An Amniocentesis Detect?
- What Are The Risks of An Amniocentesis?
- Choosing If An Amniocentesis Is Right For You
- What Do I Expect During An Amniocentesis?
- What Happens to The Removed Fluid?
- When Do I Get The Results of An Amniocentesis?
- What Happens If a Problem is Found?
- Treating Defects Diagnosed by An Amniocentesis
What Is An Amniocentesis?
An amniocentesis is a prenatal test that is performed by your health practitioner to gather information about your baby’s health and development from a sample of your amniotic fluid, the fluid that surrounds your baby in the womb. During your baby’s growth skin cells are shed that remain in your amniotic fluid along with other substances, such as alpha-fetoprotein (AFP).
During an amniocentesis a small amount of amniotic fluid is removed from the sac surrounding the fetus. The sample of amniotic fluid is less than an ounce and is removed through a fine needle inserted into the uterus through the abdomen, under the guidance of an ultrasound.
Why Is An Amniocentesis Performed?
There are a few reasons why your health practitioner may perform an amniocentesis:
- To diagnose or rule out a uterine infection.
- You have had an abnormal ultrasound.
- You have a family history of specific birth defects.
- You have previously had a child or pregnancy with a birth defect.
- You will be 35 years old or older at the time of delivery.
Having an amniocentesis presents a small risk to both Mother and baby, therefore the prenatal test is usually offered to women who have a significant risk for genetic diseases.
An ultrasound is performed at the same time of your amniocentesis which will aid in detecting birth defects such as a cleft palate, cleft lip, club foot, or heart defects. Though an amniocentesis is a highly sophisticated procedure, there are still birth defects that may not be detected by either an ultrasound or amniocentesis.
If you are having an amniocentesis, ask to find out the sex of the baby. An amniocentesis is the most accurate way to determine the baby’s gender before birth.
When Is An Amniocentesis Performed?
Typically an amniocentesis is performed between the fifteenth (15th) and eighteenth (18th) week of pregnancy.
During the third trimester, it is not uncommon to have an amniocentesis if an early delivery is needed for your baby. An amniocentesis will help, in this case, to determine that your baby’s lungs are mature enough for delivery.
How Accurate Is An Amniocentesis?
Though an amniocentesis may occasionally be unsuccessful due to technical problems like being unable to collect enough amniotic fluid or failure of the collected cells to grow when cultured, the accuracy of an amniocentesis is about 99.4%.
What Disorders & Defects Can An Amniocentesis Detect?
An amniocentesis is used to detect the following:
- Several hundred genetic disorders including but not limited to, cystic fibrosis, sickle cell disease, and Tay-Sachs disease. An amniocentesis is not used to test all genetic disorders but if your baby is at an increased risk of having one or more genetic disorders, in most cases, an amniocentesis can tell you whether your baby has the disease.
- Chromosomal disorders including Down syndrome, Trisomy 13, Trisomy 18, Trisomy 21, sex chromosome abnormalities (such as Turner syndrome and Klinefelter syndrome). An amniocentesis is more than 99% accurate in diagnosing these conditions.
- Neural tube defects such as spina bifida and anencephaly.
The amniocentesis itself does not detect birth defects such as heart malformations or a cleft lip/palate but the ultrasound during the amniocentesis is used to detect such birth defects.
An amniocentesis can also provide access to DNA for paternity testing prior to delivery. DNA is then collected from the potential father and is compared to the DNA obtained from the baby during the amniocentesis. The results are accurate for determining paternity (99%).
What Are The Risks of An Amniocentesis?
An amniocentesis is considered to be both a safe procedure and an invasive diagnostic test. With that, potential risks are involved.
- Cramping & Vaginal Bleeding: After an amniocentesis cramping is possible. Some women also experience a small amount of vaginal bleeding.
- Needle Injury: During the amniocentesis your baby may move an army or leg into the path of the needle, serious injuries are rare.
- Rh sensitization: If you have Rh negative blood and the amniocentesis causes the baby’s blood cells to enter the Mother’s bloodstream, you’ll be given a drug called Rh immunoglobulin after an amniocentesis to prevent you from producing antibodies against your baby’s blood cells.
- Infection: Though very rare, an amniocentesis may trigger a uterine infection.
- Miscarriage: An early amniocentesis carries a slight rsk of miscarriage, often due to rupture of the amniotic sac. The highest risk of miscarriage when the procedure is done early in pregnancy, before the two layers of fetal membranes have sealed. However, during the second trimester, the risk of miscarriage is generally considered to be one in two hundred (200).
A genetic amniocentesis is typically offered when the test results of the amniocentesis may have a significant impact on the management of the pregnancy. Make your decision to have a genetic amniocentesis with your health care provider, your genetic counselor, and your partner/family.
Maturity amniocentesis is typically suggested when early delivery would be best for the Mother. With minimal risks, maturity amniocentesis can offer assurance that the baby is ready for birth and the lungs have matured enough for the baby to survive outside of the womb.
If, after an amniocentesis you develop a fever or if vaginal bleeding or uterine cramping lasts more than several hours, contact your health care provider.
Choosing If An Amniocentesis Is Right For You
Reasoning for testing and not to test varies from Mother to Mother and couple to couple. Performing an amniocentesis and confirming the diagnosis provides you with specific opportunities including:
- Begin planning for a child with special needs.
- Start addressing anticipated lifestyle changes.
- Make a decision about carrying the child to term.
- Pursing potential interventions (i.e. fetal surgery for spina bifida).
There may be reasons that an amniocentesis is not right for you including:
- Being comfortable with the results, regardless of the outcome.
- Personal, moral, or religious reasons about making a decision to carry the child to term is not an option.
- Choosing not to allow testing that poses any risk of harming the developing baby.
It’s important to discuss both the risks and benefits thoroughly with your health care provider before making the decision to have an amniocentesis. Your health care provider will help you evaluate if the benefits from the results could outweigh any possible risks from the procedure.
There is no one right decision to make when considering an amniocentesis. Individual Parents-to-Be have different feelings about what risks are acceptable and thus may arrive at different conclusions.
What Do I Expect During An Amniocentesis?
An ultrasound will be performed before your amniocentesis begins to measure your baby and check basic anatomy. Some testing centers may perform this ultrasound when you come in for your amniocentesis while others may perform this ultrasound in advance.
During the Amniocentesis Procedure
You will lie flat on an examination table and your belly will be cleaned with alcohol for an iodine solution. Generally, an anesthetic is not used during an amniocentesis as most women report only mild discomfort during the procedure, similar to having blood drawn.
An ultrasound will be used to locate your baby’s exact position and pinpoint a pocket of amniotic fluid a safe distance from both the baby and the placenta.
Once the position of your baby and the placenta has been determined, under ultrasound guidance, your doctor will insert a long, thin, hollow needle through your abdominal wall and into the sac of fluid around your baby.
About an ounce or two tablespoons of amniotic fluid will be drawn and then the needle will be removed. Withdrawing the fluid can take a few minutes but typically lasts only 30 seconds.
Do not worry about the fluid that was removed, your baby will make more fluid to replace what has been taken out.
During an amniocentesis the amount of discomfort you may feel will vary. Some women feel cramping, pinching, or pressure while others feel no discomfort at all. The amount of pain varies for all women and even from one pregnancy to the next.
After the Amniocentesis Procedure
Your health care provider may use the ultrasound to monitor your baby’s heart rate or use an external fetal monitor to listen to the baby’s heartbeat.
You may be advised to rest and may need someone to drive you home from the appointment. Avoid heavy lifting, intercourse, exercise, and air travel for the next one to three days.
From start to finish, the entire procedure typically lasts one hour though most of that time is devoted to the ultrasound.
What Happens to The Removed Fluid?
Skin cells from the fetus and the amniotic fluid can be analyzed. Cells are separated from the amniotic fluid and grown in a laboratory for 10 to 12 days. The cells are then tested for chromosomal abnormalities or genetic birth defects.
The levels of the protein alpha-fetoprotein (AFP) in the amniotic fluid can be meausred to help diagnose neural tube defects (NTDs). AFP levels are often increased when the baby has a NTD. Results from this test are usually available in a few days.
When Do I Get The Results of An Amniocentesis?
The full results from the test are typically available within two weeks.
In some cases, you may be given preliminary results while you’re waiting for the skin cells to reproduce in the laboratory. Preliminary results are typically available quickly, often in a couple of days.
What Happens If a Problem is Found?
If a problem is discovered in your amniocentesis results, you will be offered genetic counseling. Counseling will help give you more information and discuss your different options. Some women opt to terminate the pregnancy while others decide to continue.
Regardless of the route you choose, you may find that you wish to have further counseling or support. Some women want individual support counseling while others find support groups helpful. Be sure to let your health care provider and genetic counselor know if you need more help so that you can be given the appropriate referrals.
Treating Defects Diagnosed by an Amniocentesis
Using medications, dietary treatments, or surgery health care providers can treat a small number of birth defects diagnosed using an amniocentesis.
Some doctors have diagnosed and treated biotin deficiency and methylmalonic acidemia (life-threatening inherited disorders of body chemistry) before birth, resulting in the birth of health babies. In most cases, however, birth defects diagnosed by amniocentesis cannot be treated before birth.
Prenatal diagnosis may help parents prepare emotionally for the birth if a birth defect cannot be treated before birth. The delivery can also be planned with your health care provider to ensure that the baby has any necessary special care right after birth.
Discuss all options with your heath care provider and/or genetic counselor.
