Genetic Amniocentesis

Genetic amniocentesis is a screening examination done during pregnancy to diagnose chromosomal abnormalities in the fetus. Usually an amniocentesis is done at between 16-20 weeks of pregnancy (gestation). During this procedure amniotic fluid is removed for testing. The amniotic fluid contains cells that the baby sheds naturally, from their skin, lungs and urinary tract. Cells and proteins within the amniotic fluid are examined in the lab to test for specific fetal disorders, such as chromosomal disorders like Down syndrome, Patau syndrome, and Turner syndrome. Alpha-fetoprotein (AFP) also found in the amniotic fluid and can be measured in the laboratory.

An amniocentesis takes approximately 45 minutes, the majority of which is during a detailed ultrasound. Ultrasound is also used during the procedure.

An amniocentesis is offered to
  • A woman who will be 35 years old or more at the time of delivery.
  • A couple with a child or other family member with a chromosomal abnormality.
  • A pregnant person who received an abnormal result from other screenings, such as the NIPT (non-invasive prenatal test), which is used to screen for chromosomal abnormalities in the fetus, such as Down syndrome. This is a blood test that can be done starting at 10 weeks of gestation.
  • A couple in which one partner has a chromosomal rearrangement (for example, a translocation or an inversion).
  • A couple with an increased risk of having a child with a genetic disease for which testing is available.
  • A couple with a child with a neural tube defect (for example, spina bifida or anencephaly).
    If you will be 35 years old or older when your baby is due and do not want an amniocentesis, speak to your doctor for alternative blood testing to screen for chromosomal abnormalities. Only certain abnormalities can be screened this way, such as those for Down syndrome. If blood tests reveal abnormalities, an amniocentesis is strongly recommended. If you still choose not to undergo the procedure, it is important you speak to your obstetrician about the possible implications and create a plan for the rest of your pregnancy and the postpartum.
  • Chromosomal disorders like Down syndrome, Patau syndrome, and Turner syndrome.
  • Alpha-fetoprotein (AFP) levels will reveal neural tube defects such as spina bifida.
  • When a history of a genetic disease is known in a family, further testing may be needed such as DNA or enzyme testing.
An amniocentesis can only detect chromosomal abnormalities and will not diagnose other congenital problems, such as problems with the heart or cleft palate. Physical deformities can usually be found through ultrasound in the second trimester, but it is also not 100% accurate in diagnosing all possible problems with the fetus. Ultrasound is only 50-70% for diagnosis of physical deformities. Most problems cannot be diagnosed by amniocentesis. Thus, genetic testing or alpha-fetoprotein (AFP) testing cannot tell with complete certainty if the fetus will be healthy.
Do not take any aspirin or aspirin-containing products five days prior to the amniocentesis procedure, and do not take anticoagulants such as heparin, enoxaparin 24 hours prior to the amniocentesis procedure.
An ultrasound is performed before the amniocentesis. You will be asked to lie on your back and expose your abdomen. (Wear comfortable clothes.) The physician will apply some jelly to your abdomen and move a transducer (a microphone-like instrument) around on your abdomen. Sound waves (not X-rays) will bounce off the tissue or fluid-filled spaces in the uterus and a two-dimensional picture will be projected on a screen. Significant features of the baby (i.e. head, spine, heart and limbs) will be pointed out to you if you would like to see them.

We use ultrasound for the following reasons:
  1. To make sure you are pregnant and there is only one baby present. If more than one baby is seen we recommend that fluid be taken from around each baby.
  2. We correlate the age of the baby with your last menstrual period. The diameter of the baby’s head is a relatively accurate way of determining age. We usually perform amniocentesis between 16 and 20 weeks from your last menstrual period. Between 16 and 20 weeks, we have the best chance of obtaining enough fluid while also allowing time to discuss options and make decisions in the event that an abnormality is detected. We will reschedule you for a later date if the ultrasound exam shows you to be less than 14 weeks pregnant.
  3. Ultrasound aids the physician in locating the safest spot to insert the needle.  We perform all genetic amniocenteses under ultrasound guidance and actually watch the needle as it is being inserted. This reduces the chances of the physician touching the baby and increases success rate of obtaining fluid. It is not unusual to delay the amniocentesis for several days if a good insertion site is not found. This does not mean that anything is wrong with the pregnancy.
  4. Once the physician has located the safest spot for the amniocentesis, the jelly is wiped off and your abdomen is sterilized with an antiseptic (betadine®). This antiseptic can stain your abdomen or clothes and should be wiped off as completely as possible. When the right location is found, the doctor will inject a local anesthetic into the skin to reduce pain. Then a thin needle is inserted into your abdomen and into the sac containing the baby. About 20 milliliters of fluid is withdrawn. Occasionally, patients feel a cramping sensation when this needle touches the uterus.
  5. It is natural to be anxious about the amniocentesis as most of us are not used to having needles inserted into our abdomen. However, almost all women say it is a lot simpler and less uncomfortable than they expected. The ultrasound examination usually takes about 20 minutes. The amniocentesis usually takes about two minutes. You are encouraged to have a support person (i.e. the baby's father) accompany you during the procedure.
  • Most women experience minimal discomfort with an amniocentesis. Some women do experience cramping during and after the procedure; the cramping usually goes away after a short time.
  • Some women may also experience abdominal soreness at the site of the needle insertion. This soreness usually goes away within a few hours, but may last a few days.
  • Sit and rest for about 30 minutes after the procedure. Medication for uterine relaxation may be administered, depending on your physician’s recommendation.
  • If you feel pain at the needle site, you may take pain-relieving medication, such as paracetamol. Please avoid taking nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or aspirin.
  • The needle site does not have to be cleaned. You can shower and bathe as usual.
  • Avoid the following activities: lifting heavy objects, walking up a flight of stairs frequently, strenuous exercise or activity, sexual intercourse for about one week after the procedure.
  • After an amniocentesis please rest at home for at least two hours. Please consider not driving yourself home after the procedure.
  • Do not fly for at least 72 hours after the procedure.
  • Avoid long-distance travel within the first week after the amniocentesis.
  • There is a natural risk for miscarriage in all pregnancies, but amniocentesis does increase that risk. The latest studies show that amniocentesis will cause miscarriage is 0.1-0.3% of cases.
  • Other rare complications include injury to the fetus, infection, and miscarriage.
If you choose not to have an amniocentesis, you must accept the risk of having a baby with congenital issues.
You should return to the hospital if you experience any of the following symptoms:
  • Severe contractions or abdominal pain. It is normal to experience some contractions after the procedure, and they should go away within two to three hours.
  • Clear watery fluid or vaginal bleeding
  • Fever higher than 38 degrees Celsius.
  • Results of the chromosome study and the alpha-fetoprotein (AFP) measurement are usually available in three weeks. Additional studies may take longer.
  • Chromosome results are greater than 99.4% accurate.
  • Alpha-fetoprotein (AFP) testing detects greater than 90% of open neural tube defects. The accuracy of any additional testing may vary depending on family history and testing method.
  • Occasionally test results may require a need for a further ultrasound examination or blood tests of the parents. Rarely a repeat amniocentesis or fetal blood sampling may be recommended.
  • There is no test that can offer a 100% guarantee that a fetus will not have congenital, genetic, or developmental problems.
Please keep in mind that all pregnancies carry the risk of a baby being born with issues. Please discuss this with a geneticist if you have any concerns. An amniocentesis is a personal decision and you must weigh the risks and benefits of the procedure before making a decision.

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