WHAT TYPES OF DISORDERS CAN BE DETECTED BY AMNIOCENTESIS?

WHO MAY BENEFIT FROM AMNIOCENTESIS?

There are a number of reasons for considering an Amniocentesis:

(1) Women in their mid-30's and over (for first and subsequent pregnancies).

(2) Women who have had a child with a chromosomal abnormality such as Down Syndrome.

(3) Women who know that they are at risk for an inherited disorder that runs in their family or the baby's father's family, which can be prenatally diagnosed.

(4) Women who have had a child with a neural tube defect such as spina bifida or who have a close relative in this situation.

 

WHY DO YOU NEED AN ULTRASOUND SCAN WITH AN AMNIOCENTESIS?

The ultrasound scan can tell the doctor if you are carrying twins, the position of the placenta and can also detect some abnormalities in the developing baby. In preparation for the Amniocentesis, the position of the baby and the location of a suitable amount of amniotic fluid are determined using ultrasound.

During the Amniocentesis the ultrasound also allows the doctor to follow the sampling procedure and ensures the Amniocentesis is carried out safely.                                                                                                                                                                                                                             

Amniotic fluid (containing fetal cells) is sampled during the 14^th - 18^th week of pregnancy.

WHAT HAPPENS DURING THE AMNIOCENTESIS?

The doctor cleans your abdomen with antiseptic fluid and inserts a very thin needle into the uterus through the abdomen. The ultrasound scan is used to monitor the position of the needle. A sample of the amniotic fluid (about 15 mls) is then withdrawn through the needle. Discomfort is usually minimal, though a very small number of patients experience pain as the needle passes through the surface of the uterus. The amniotic fluid contains cells shed by the developing baby. These cells are allowed to grow and multiply in a laboratory until there are enough to test.

WILL THE AMNIOCENTESIS HAVE TO BE REPEATED?

Very occasionally, more than one Amniocentesis is necessary to obtain a diagnosis. This happens when the doctor is unable to obtain enough fluid on the first attempt, or when the laboratory is unable to make an analysis of the fluid.

ARE ANY OTHER TESTS NECESSARY?

Where there is uncertainty about the results of the Amniocentesis, or a rapid result is required, Cordocentesis, also called Fetal Blood Sampling or FBS) may be recommended as a prenatal test.

This test is used for the diagnosis of infection and some specific disorders. A sample of the baby's blood is taken by passing a fine needle into the umbilical cord using ultrasound guidance. There is a miscarriage risk related to the test of about 2% (1 in 50 pregnancies), but may be higher if there are other problems associated with this pregnancy.

WHAT WILL THE AMNIOCENTESIS TELL US ABOUT THE BABY?

Doctors and scientists are now able to diagnose a large number of disorders prenatally. It is not feasible to test the cells for all the possible abnormalities that could affect the baby. Discuss with your doctor the range of disorders which might be detected.

WHEN WILL THE AMNIOCENTESIS BE DONE?

The test is usually performed during the 14th to 18th week of pregnancy. At this time, there is enough amniotic fluid to sample.

WHERE WILL THE TEST BE DONE?

Amniocentesis is an outpatient test, performed by doctors who are experts in doing this procedure. All Amniocentesis are performed at 2 Hay St (see map) unless you are told otherwise.

WHEN WILL THE TEST RESULTS BE AVAILABLE?

The results are usually available in 2 to 3 weeks. When the Amniocentesis is done for the diagnosis of neural tube defects, the results may be available sooner.  Rapid testing (results within 2 days) for the major chromosomes that are involved in abnormal results (21,13,18,X, Y)is available. Unfortunately this is not covered by medicare.

DOES THE AMNIOCENTESIS HARM THE PREGNANT WOMAN OR THE UNBORN CHILD?

If the Amniocentesis is done by a doctor experienced in this technique, the risk of miscarriage related to the test is less than 1% (1 in 100 pregnancies), including those patients who would have miscarried without a test. If a miscarriage does occur, it usually starts within a couple of weeks of the test.

It is not uncommon to experience mild cramping on the day of the test. However, a small number of women may experience bleeding and some leaking of amniotic fluid. You should contact your doctor if this occurs. Most women have no symptoms or pain at all after the procedure.

Parents are often concerned that the needle will hurt the baby, but the use of the ultrasound during the procedure enables the needle to be inserted in a position away from the baby. All procedures are carried out under sterile conditions.

WHAT HAPPENS IF THE RESULTS OF THE AMNIOCENTESIS SHOWS AN ABNORMALITY IS PRESENT IN THE BABY?

Most often, the baby will not have the particular disorder for which it was tested. When the test does show that the baby has an abnormality, the expectant parents will be given as much information as possible to enable them to make a choice about whether to continue the pregnancy.

Support and information is available to the expectant parents at this time. Genetic counselling is recommended.

If the parents do decide to terminate the pregnancy following the diagnosis of a serious birth defect, the procedure requires hospitalisation. The method of termination will vary depending on the policy of the particular hospital or clinic. It may involve an induction of labor and birth or a procedure known as D and E (Dilatation of the cervix and Evacuation of the uterus). All aspects should be fully discussed with your doctor. Counselling is also available to assist you.