To whom is amniocentesis offered?
The most common situations in which amniocentesis is offered are:
- Maternal age: The risks of certain chromosomal abnormalities increases as a woman ages. Currently, all pregnant women are offered Down Syndrome screening tests in the first or second trimester which can give a more accurate prediction than age alone of the likelihood of chromosomal abnormalities. This likelihood can then be used to determine whether she is a candidate for additional diagnostic testing by amniocentesis; however, a woman does have the option of proceeding directly to amniocentesis , without prior screening tests, if she chooses.
- Prior obstetric history: If a woman has had a prior child with certain types of chromosomal abnormalities or genetic defects, the recurrence risk may be high enough to warrant definitive testing in subsequent pregnancies by amniocentesis.
- Abnormal screening test results: All pregnant women are offered screening tests for chromosomal abnormalities. These tests predict an individual patient’s likelihood of having a baby with certain chromosomal abnormalities and this risk level is then used to determine whether she would be a candidate for further, definitive testing such as amniocentesis. Most babies that are born with chromosomal abnormalities are born to women with no prior history or family history of problems, and that is why the screening tests are used to more accurately predict an individual patient’s risk.
- Family history: If there is a family history of a genetic or chromosomal abnormality that can be detected by amniocentesis, and there is enough recurrence risk to warrant an amniocentesis, the patient would be offered amniocentesis for further testing.
- Ultrasound abnormalities: If certain abnormalities are seen on an ultrasound (for example, a heart abnormality), amniocentesis may be considered to determine if a chromosome problem might be the cause of the abnormality
- Pregnancy complications: Amniocentesis is frequently used to evaluate complicated pregnancies. Amniocentesis can be used to detect some types of fetal infections; blood incompatibilities between mother and baby; or to determine if the baby's lungs are mature if an early delivery is being considered.
When is amniocentesis done?: Amniocentesis can be performed any time after 14-15 weeks of pregnancy. Usually, if it is being performed for detection of genetic or chromosomal abnormalities, it is performed between 15 and 18 weeks gestation. In other situations, such as when it is being performed for evaluation of blood incompatibility problems or lung maturity, it can be performed anytime that your care giver thinks it would be helpful in the management of your pregnancy.
How is Amniocentesis performed?: Ultrasound is first used to look at the baby’s position, size, anatomy, etc. The placental location and amniotic fluid volume are also evaluated. Using ultrasound, the physician and ultrasound technician can then find an area of amniotic fluid that is safe for sampling. A thin needle is then placed through the maternal skin and lower abdominal wall, and ultrasound is used to guide the needle into the pocket of fluid. Two or three tablespoons of fluid are then removed and sent for testing. The procedure takes about 45 seconds to perform and, in over 99% of cases, requires only one pass of the needle to obtain the fluid. Most patients describe the discomfort as a “crampy” sensation that generally resolves within a few minutes of the procedure.
What are the risks of Amniocentesis?: One concern that patients sometimes have is whether the baby could be injured by the needle; this is extraordinarily rare since ultrasound is used to show precisely where the needle will be and where the baby is. We have never had a needle injury to a fetus at Rocky Mountain Perinatal Associates. There is an extremely small risk of miscarriage associated with the amniocentesis. Recent research in which amniocentesis was performed by specialists in units performing a high volume of procedures suggests that the miscarriage risk due to amniocentesis is 1:1000 or less. The staff of Rocky Mountain Perinatal Associates has performed thousands of amniocentesis procedures.
Are there any special instructions following amniocentesis?: Generally, patients are advised to refrain from strenuous activities on the day of the procedure, such as workout/exercise regimens or jobs that require prolonged standing or heavy lifting. Patients can return to their normal routine and activity levels on the day following the procedure.
How long does it take to get results?: Generally, complete diagnostic results take between 10 and 14 days to return. The staff of Rocky Mountain Perinatal Associates will call you immediately when the results are available.
Can amniocentesis detect all birth defects?: It is important to remember that 3% to 4% of all newborns are eventually found to have some type of birth defect. Many of these defects are detectable by techniques such as amniocentesis or ultrasound, but some birth defects cannot be detected by any technique before birth, no matter how much testing is done. Therefore, a normal amniocentesis is not a guarantee of the birth of a normal baby; however, the specific abnormalities for which amniocentesis is performed can usually be definitively diagnosed or excluded by the procedure.
Is treatment available for abnormalities detected by Amniocentesis?: Unfortunately, most abnormalities detectable by amniocentesis cannot be treated before birth nor can the exact outcome for an abnormality be predicted. Many patients still choose to have testing, so that they can have more information about the abnormality. Also, many patients feel that it is helpful for them emotionally to be able to prepare themselves or their family for the birth of a child that may have birth defects or other problems. Sometimes, such knowledge is helpful so that the baby can be born in an environment (for example, a hospital with a neonatal intensive care unit) that is better able to care for a child with a birth defect. When an abnormality is detected by amniocentesis, you will be offered further counseling to discuss the results, the possible outcomes for your pregnancy, and how the abnormality might affect the medical management of your pregnancy.
Should I have Amniocentesis?:As described above, not all patients are candidates for amniocentesis since there is a small risk associated with the procedure. Generally, your obstetrical caregiver will be discussing your history and screening test results with you to help determine whether you are a candidate for an amniocentesis. It is important to remember that an amniocentesis is never a required test, even if you are at increased risk for chromosomal abnormalities. Only you, after having appropriate counseling and discussions with your obstetrical caregiver, a perinatologist, or genetic counsellor can decide whether amniocentesis is right for you.
