Aminocentesis

Amniocentesis is a test done on fetal cells and is usually offered to women over 35. However, this guideline is currently being challenged.

What the Test Can Detect
Most women who have amniocentesis are being screened for chromosomal defects, such as Down syndrome, Turner's syndrome or neural-tube defects (spina bifida]. The test can pick up some specific gene defects, including cystic fibrosis and sickle cell disease. Other problems amniocentesis can identify include the following:
•    skeletal diseases, such as osteogenesis imperfecta
•    fetal infections, such as herpes or rubella
•    central-nervous-system disease, such as anencephaly
•    blood diseases, such as erythroblastosis fetalis
•    chemical problems or deficiencies, such as cystinuria or maplesyrup-urine disease


Amniocentesis can determine the baby's sex. However, the test is not used for this purpose, except in cases in which the sex of the baby could predict a problem, such as hemophilia. Amniocentesis may be performed to see if the baby of an Rh-negative woman is having problems, and it may be done to determine fetal lung maturity before delivery.
It may be a good idea to have amniocentesis if your doctor suggests it, even if you would not end your pregnancy should results indicate a problem. If a problem is detected, you and your family can prepare for it. You can gather information about the problem.

The test may also indicate the need for additional tests to determine if the fetus might have other problems. If any are found, steps can be taken to ensure the delivery goes smoothly and any necessary procedures are done as soon after the birth as possible.

Who Receives Amniocentesis?
Not every pregnant woman needs amniocentesis. It is often performed on women who fit any of the following criteria:
•    they will deliver after their 35th birthday
•    they have had a previous baby with a birth defect
•    they have a family history of birth defects
•    they have a birth defect themselves
•    thier partners have a birth defect


How the Test Is Performed
Ultrasound is used to locate a pocket of fluid where the fetus and placenta are out of the way. Skin over the mother's abdomen is cleaned and numbed with a local anesthetic. A needle is passed through the abdomen into the uterus, and fluid is withdrawn with a syringe. About 1 ounce (0.029 L) of amniotic fluid is needed to perform the tests. The test can identify about 40 fetal abnormalities.

Risks with Amniocentesis
Although risks are relatively small, there is some risk associated with the procedure, including trauma to the fetus, placenta or umbilical cord; infection; miscarriage or premature labor. Fetal loss from complications is estimated to be between 0.3 and 3%.
Discuss the risks with your doctor before the test. Only someone with experience, such as a physician at a medical center, should perform amniocentesis.

In a multiple pregnancy, genetic testing can be a complicated procedure. For example, in most multiple pregnancies, each baby lies in its own sac. Double abdominal punctures are required to withdraw fluid from each of these sacs, which can increase the risk of cornpli ations. In the case of one sac shared by the two babies, only one amniocentesis is performed.

Disadvantages of the Test
The greatest disadvantage of the test is the time at which it is performed. Amniocentesis is usually performed for prenatal evaluation at around 16 weeks of pregnancy, making termination of a pregnancy (if that is what the woman chooses) more difficult. Some doctors are now performing the test at around 11 or 12 weeks. However, this early use is considered experimental.