Amniocentesis is a method of prenatal testing which has been performed on several hundred thousand women over a 20 year period.

Who should consider amniocentesis?

Amniocentesis should generally be considered by women age 35 or older at the time of delivery, individuals who have had a child with a chromosomal abnormality, individuals who have a chromosomal translocation, couples at risk for a prenatally indentifiable disorder associated with genetic alterations (e.g., hemophilia or sickle-cell disease), and individuals who have had a child or another family member with a neural tube defect (spina bifida or anencephaly).

When is amniocentesis performed?

Standard amniocentesis is performed between 15-18 weeks after a woman's last menstrual period. It can, however, be performed at later stages if necessary. A newer procedure called early amniocentesis is performed between 13-15 weeks after a woman's last menstrual period.

• Women who are less than 13 weeks pregnant may wish to consider pursuing a chorionic villus sampling procedure instead of amniocentesis.
• Women who are between 13 and 15 weeks pregnant may wish to consider late CVS or early amniocentesis.

How is amniocentesis performed?

An ultrasound evaluation is performed to assess fetal development, to locate the placenta, to determine fetal age, and to select a pocket of amniotic fluid. A site is marked on the woman's abdomen and with ultrasound guidance, a thin needle is inserted through the abdomen into the uterus. A small amount of amniotic fluid is removed and sent to be analyzed.

Does the procedure hurt?

Most women describe the procedure as somewhat uncomfortable. Some women do experience cramping after the test. Most women are able to return to normal activities shortly after the test.

What is the risk of miscarriage after amniocentesis?

For standard amniocentesis, the most common complications are vaginal spotting or bleeding, severe cramping, or miscarriage. Infection is not very common and occurs in less than 1 in 1000 cases. The risk for complications with the procedure is 1/2 percent above the natural complication rate for this period in pregnancy. In early amniocentesis, the risks are still under study, but appear to be approximately the same.

What is analyzed from amniocentesis?

Cells shed from the amnion (the sac surrounding the fetus), fetal skin, and gastrointestinal tract are normally floating in the amniotic fluid. These cells can be grown (cultured) in the laboratory. Chromosomal analysis is performed on these cultured cells. AFP (alpha-fetoprotein) is also present in the amniotic fluid and is measured.

What can be detected through amniocentesis?

Chromosomal abnormalities (such as Down syndrome) may be detected through amniocentesis. The majority of neural tube defects are detected by elevated levels of AFP in the amniotic fluid. Some genetic alterations responsible for genetic disorders may be identified through DNA or enzyme analysis if indicated. While the prenatal CMA test is very accurate, not every genomic abnormality (genetic defect) can be detected by a prenatal CMA test. For some conditions, genomic gains or losses at a particular locus may represent only a certain percentage of the genetic changes associated with that given disorder. For instance, in some disorders, 99% of the cases may be detected by the test, while for others the detection rate may be 70% or less. No method of prenatal testing can guarantee a baby will be born without birth defects or genetic disorders, nor does every genetic alteration have profound clinical consequences. For this reason, results from your tests should be thoroughly discussed with clinicians, genetic counselors and other qualified medical personnel.

How accurate are the results from amniocentesis?

Chromosome results are greater than 99% accurate. In standard amniocentesis, amniotic fluid AFP is greater than 90% accurate in detecting neural tube defects. The detection of neural tube defects by early amniocentesis has yet to have its accuracy verified. Occasionally, results need to be clarified through blood tests on the parents, ultrasound, a repeat amniocentesis, or fetal blood sampling.

How long will the results take?

Chromosome and amniotic fluid AFP results take approximately two weeks for completion. Special studies for other genetic disorders may take longer.

How many appointments are needed?

All women will be scheduled for a genetic counseling session to discuss the procedure in detail, determine whether additional genetic testing is appropriate, and ensure that all concerns have been addressed. Those selecting amniocentesis are scheduled for the procedure between 15-18 weeks. These two appointments may be scheduled on the same day.