• 1st Trimester Genetic Risk Assessment
• Maternal Screening
• Chorionic Villous Sampling
• Genetic Amniocentesis
• Cystic Fibrosis Carrier Screening
• Integrated Prenatal Screening

Genetic Amniocentesis

Amniocentesis involves the withdrawl of amniotic fluid through a fine needle which is inserted through the mother's abdomen and into the amniotic sac (bag of waters) surrounding the baby.  This fluid contains cells shed from the baby's skin, lungs and urinary tract.  These cells and fluid may then be analyzed for certain genetic problems.

What can prenatal diagnosis tell me about my baby?

1.  Chromosomes

Chromosomes are tiny packets of information that carry the genes that code for our growth and development.  There are 46 chromosomes in most normal cells in our body.  In the Cytogenetics Laboratory, the baby's cells from the amniotic fluid are cultured (grown) and the chromosomes in about 20 cells are analyzed.  Sometimes, we find either additional or missing chromosomal material that indicates the baby may be born with abnormalities.  Chromosome analysis will be able to identify not only Down syndrome (in which there are 47 chromosomes because of an additional number 21 chromosome), but also other types of chromosomal abnormalities in the baby.

2.  Neural Tube Defects

The Department of Laboratory Medicine will measure a chemical known as Alpha-feoprotein (AFP) in the amniotic fluid.  This protein, AFP, is normally present in the amniotic fluid in small amounts.  However, if there is an opening along the spinal cord or brain (spina bifida or anencephaly), it may leak out in large amounts causing abnormally high levels in the amniotic fluid.  Ninety-five percent of open neural tube defects may be detected by amniocentesis.  In the general population, the chance of having a child with a neural tube defect is about 1-2 per 1,000.

3. Other Information

In addition to the chromosome analysis and biochemical test for neural tube defects, there are several hundred other conditions that could be performed on the amniotic fluid (such as muscular dystrophy, cystic fibrosis and sickle cell anemia).  However, because of the limited amount of fluid and excessive cost of these additional tests, they are not performed routinely on all amniotic fluid samples.  This is why it is important for the Genetic Counselor to take a family history and identify any additional risks prior to having the procedure.

What amniocentesis will not tell us:

It is important to realize that no test can detect all birth defects.  There is a 3-5% chance that any pregnancy may end with a child with a birth defect (such as heart defect or cleft lip).  Most of these defects are not detectable by amniocentesis.  Thus, a normal chromosome test or AFP does not necessarily guarantee a normal baby.

What is the procedure like?

We perform an ultrasound examination before the amniocentesis.  You will be asked to lie down on your back and expose your abdomen.  (Wear comfortable clothes.)  The ultrasonographer will apply some warmed, water-soluable 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 the ultrasound examination for the following reasons:

1.  We 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.  A measurement of the baby,s head diameter is a relatively accurate way of determining age.  We usually perform amniocentesis between 16 and 18 weeks from your last menstrual period.  Between 16 and 18 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.  In this way, we reduce the chances of touching the baby and increase the 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.

Once the Ultrasonographer and Perinatologist have located the safest spot for amniocentesis the jelly is wiped off and your abdomen is cleansed with an orange colored antiseptic (betadine).  This antiseptic can stain your abdomen or clothes and should be wiped off as much as possible.  After this, a thin needle is inserted into your abdomen and into the sac containing the baby.  About 2 tablespoons of fluid are withdrawn.  Occasionally, patients feel a cramping sensation when this needle touches the uterus.

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 not as uncomfortable as they expected.  The ultrasound examination usually takes about 20 minutes.  The amniocentesis usually takes about 2 minutes.  You are encouraged to have a support person (i.e. the baby's father) accompany you during the entire procedure.

What do I need to do before and after the procedure?

There are no special instructions before the procedure.  After amniocentesis, we suggest that you avoid heavy lifting and strenuous activity for about 24 hours.  You may resume any other normal activities.  Immediately after the procedure, you will probably feel more comfortable if someone drives you home.

What are the problems associated with amniocentesis?

Our experience has shown that the risk of amniocentesis is small when performed at our center (about 1 in 400 for miscarriage).  There is no evidence that the removal of amniotic fluid in pregnancy has any long term effect on the baby.  In fact, the fluid consists mainly of fetal urine which is quickly replenished.  Specific risks for problems will be discussed during your counseling session.

When and how will I receive my results?

Results are usually available 2 to 3 weeks after amniocentesis.  We will phone you as soon as we receive your results.  It is normal to feel anxious while waiting for your tests to come back.  Please let us know if you do not want to know the sex of the baby.  Your doctor will be informed by mail.

In the event that there is an unusual result, you and the baby's father will be contacted by phone.  We will ask you to come in so that we may explain that we know about the abnormality and discuss your options with you.  We will offer you support in your decision and provide you with referral sources if you would like them.  Some people choose to terminate a pregnancy based on abnormal finding.  Others decide to continue the pregnancy but feel that the advance knowledge helps them prepare both themselves and others for a child who may have special needs.  Most women have normal results and never have to make these decisions.

IN CONCLUSION

We firmly believe that all women at increased risk to have a baby with a problem should receive Genetic Counseling.  But we feel that the decision to have an amniocentesis is a personal matter.  You must decide what is best for you by weighing the risks of the procedure against the benefits of obtaining the information.  We hope this information has been helpful.  Please feel free to contact us if you have any questions.

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Last Updated:
4/29/08