Amniocentesis

Before making a choice about prenatal testing, it is helpful to understand the purpose, benefits, limitations, risks and consequences of testing. This information outlines the important information you need to help you decide if you want to have amniocentesis testing.

• Most babies are born healthy regardless of a woman’s age, family history, ethnic background or if prenatal testing was done during her pregnancy.
• Every couple has a 2–3 percent chance of having a baby with some type of birth defect (such as a heart defect, clubfoot, cleft palate). Some birth defects can be corrected after birth and will have little effect on the child’s overall health and development. Other birth defects can be more serious to the child’s overall health. Not all birth defects can be detected in pregnancy.
• Having any prenatal testing in your pregnancy is your choice. Make sure to ask your genetic counsellor or prenatal care provider your questions before making your decision.

What is amniocentesis?

Amniocentesis is medical procedure performed by a doctor that diagnoses chromosome conditions and identifies pregnancies at risk for neural tube defects (an explanation on these conditions is given at the end of this information) . A diagnostic test for chromosome problems means that most of the time, the test will give a definite “yes” or “no” answer to whether a baby has a chromosome condition. Amniocentesis is also very helpful in ruling out most of the serious neural tube defects.

Is amniocentesis safe?

Most women do not have complications after their amniocenteses. However, there is a risk of miscarriage with the test. For every 200 amniocentesis done, one pregnancy (0.5 percent) will be lost to miscarriage due to the procedure. Cramping may occur for a short while after the procedure. There may be a very small amount of vaginal spotting. Leaking amniotic fluid through the vagina is uncommon. Because amniocentesis is done using sterile conditions, infection is veryrare. If you have any problems, contact your prenatal care provider.

Who is offered amniocentesis?

• are 35 years of age or older (see Table 1).
• have an increased risk prenatal screening test result from First Trimester Combined Screening, Nuchal Translucency Screening, Maternal Serum Screening or second trimester ultrasound. (A risk greater or equal to 1/300).
• have a family or personal history that places their pregnancy at increased risk.

When is amniocentesis done?

Amniocentesis is usually done between 15 and 18 weeks of pregnancy, although earlier or later amniocentesis will sometimes be done.

How is amniocentesis done?

An ultrasound is used to locate your baby’s position. An ultrasound is not an x-ray and is considered safe for both you and your baby. The procedure is closely followed by ultrasound to make the procedure as safe as possible for both you and your baby. A fine needle is carefully inserted through your abdomen and one to two tablespoons (15-30 mL) of fluid is removed for testing. The ultrasound is continued throughout the test to monitor the baby’s heartbeat. The actual test usually takes only a few minutes. After the test is finished you will need to arrange for a ride home. Take the rest of the day off. However, you do not need to stay in bed unless your doctor says otherwise.

How do I prepare for amniocentesis?

You will be asked to attend a pre-test information session. The session will go over the risks, benefits, and limitations of the procedure. You will be able to ask any questions you may have.

You do not have to do anything to prepare on the day of your test. When you arrive for your appointment, please do not empty your bladder until one of our staff asks you to.

What happens after the procedure?

Avoid strenuous activity (e.g. vacuuming) for a day after the procedure. You may have a small amount of bloody spotting for up to a week.

• a fever
• painful contractions or worsening abdominal pain.
• unusual or bloody drainage from the vagina (If you have vaginal discharge, wear a sanitary pad and bring it in to show your doctor.)

What are the benefits of amniocentesis

For the most part, the results from amniocentesis are reassuring, giving you peace of mind for the rest of the pregnancy.

What can affect the results of the test?

• a technical difficulty getting an amniotic fluid sample
• the cells do not grow, so no result is possible
• trouble interpreting the test results (you and your partner may be asked to give a blood sample to help interpret your baby’s chromosome result)

How long do results take?

Results of amniocentesis take 2-3 weeks. Your family doctor or the obstetrician who did your test will review the result with you.

Do normal amniocentesis results mean that the baby will be born healthy?

No prenatal test can guarantee the birth of a healthy baby. Of 100 babies are born, 2 to 3 will have a birth defect that cannot be diagnosed with amniocentesis.

What happens if a chromosome condition is detected?

Genetic counselling and support are available. This is provided through your prenatal care provider and/or the PrenatalGenetics Clinic. The purpose of the counselling is to review the results and provide all the support and information necessary to help you and/or your partner make decisions about your pregnancy management.

Is there a diagnostic test for chromosome conditions available earlier in pregnancy?

Chorionic Villus Sampling is another prenatal diagnostic test available for eligible women between 11 and 13 weeks of pregnancy.

What are the differences between CVS and amniocentesis?

• CVS can be done earlier (at 10-13 weeks). Amniocentesis is done after 15 weeks.
• You usually have the results before your 15th week of pregnancy.
• CVS removes tissue from the developing placenta. Amniocentesis removes amniotic fluid surrounding the baby.
• Amniocentesis screens for neural tube defects: CVS does not. However, the recommended 18-20 week ultrasound will pick up most serious birth defects, including neural tube defects.
• The risk for miscarriage may be slightly higher with CVS (1%) than with amniocentesis (0.5%).

If I choose not to have an amniocentesis what other options do I have?

• If you chose not to have amniocentesis, keeep in mind that the chances are in your favour that your baby does not have a chromosome problem.

• The First Trimester Combined Screen is done between 11 to 13 weeks and 6 days of pregnancy. The Maternal Serum Prenatal Screen is done between 15-20 weeks of pregnancy.
• An 18-20 week ultrasound to assess the growth and development of the baby, rule out major birth defects and check for signs that may suggest a chromosome condition.

What are chromosome conditions and Neural Tube Defects?

The web page Understanding Chromosome Conditions and Birth Defects provides you with this information.

Table 1: Risk for having a baby with a chromosome condition based on maternal age

Age At Delivery	Down syndrome risk in mid-pregnancy*	Down syndrome risk at term	Term risk for any significant chromosome abnormality (including Down syndrome)
25		1/1250	1/476
26		1/1176	1/476
27		1/1111	1/455
28		1/1053	1/435
29		1/1000	1/417
30	1/630	1/952	1/384
31		1/909	1/384
32	1/460	1/769	1/322
33		1/625	1/317
34	1/310	1/500	1/260
35	1/250	1/385	1/204
36	1/200	1/294	1/164
37		1/227	1/130
38	1/120	1/175	1/103
39		1/136	1/82
40	1/70	1/106	1/65
41		1/82	1/51
42	1/40	1/64	1/40

* the chromosome risk is greater at the mid-trimester of pregnancy as many pregnancies carrying a baby with a chromosome condition are lost to miscarriage before term.

Of note - the chance of having a baby without a chromosome condition are always in a woman's favor. For example, a 35 year old woman has a 99.5% chance at term that her baby would not have a chromosome condition. A 42 year woman has a 97.5% chance of a baby with normal chromosomes.