Amniocentesis: How Do I Know If I Really Need One?

Amniocentesis: How Do I Know If I Really Need One?
Family Digest Baby magazine, Holiday 1999
Reprinted with permission from Family Digest Baby magazine.

An amniocentesis is a prenatal test used to diagnose genetic or neural defects before the baby is born. This procedure is done via ultrasound guidance when a small needle is placed through the abdominal wall and into the uterine cavity. A small amount of fluid is aspirated and sent to the lab for chromosome/genetic and chemical testing. This procedure is usually performed at 15 to 20 weeks from the Last Menstrual Period. Some centers perform the test earlier depending on the provider experience and comfort level. An ultrasound needs to be done at the same time in order to verify viability, number of fetuses, location of placenta, amount of amniotic fluid, and gestational age. Ideally the placenta is not pierced during the process. During and after the procedure the fetus is observed for well being. Approximately 4 teaspoons of fluid is sent to the lab. The results generally take between 10 to 14 days.

How safe is this procedure?
The maternal risks for this procedure are very low with less than 0.1% getting an infection. Rarely, 1-2 % of patients may experience vaginal spotting or amniotic fluid leakage. These problems usually are short lived and resolve. Any woman who has a blood type which is Rh- and unsensitized (has had no previous pregnancy problem with blood type incompatibility between mother and fetus) needs to receive Rh-immune globulin to prevent sensitisation in the future. Most centers counsel patients that the risk of miscarrage due to the procedure is less than 1%. This procedure is relatively safe in skilled hands; in those who perform the procedure several times a month.

Should I have an amniocentesis?
This testing is offered to women who are 35 and older at the time of delivery. Although it is the standard of care to offer this testing at the age of 35 this number is somewhat arbitrary and chosen only because of the standard 5 year intervals used to report the risk of abnormal babies. This testing is also indicated in a patient with a previous child with a chromosomal abnormality, or in parents with a known chromosomal abnormality. Amniocentesis will be offered to those who have the abnormal blood test, AFP or Triple marker screen. This blood test looks for those at higher risk for chromosomal defects or neural tube defects (abnormalities in the brain or spinal cord). For example if a women would like to know if her baby will have Sickle cell anemia or Thalesemia, and she is a carrier, this can be detected by amniocentesis. These are two common hemoglobin abnormalities in people of color.
The more important question in pursuing any prenatal diagnosis is what the mother-to-be would do with the information. The range of responses includes just wanting to be prepared for a child with special needs, to termination of the pregnancy pending the results. This is an issue which should be discussed with your provider before this testing is done, just to go over the different scenarios regarding the outcome. This team effort between you, the doctor, and the support people in your life will help you to make the right decison for you.

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