Chromosome Abnormalities

The standard laboratory testing detects over 99% of all chromosome abnormalities. The results are usually ready within 14 days.

Missing or extra chromosomes lead to serious physical birth defects, mental [4] retardation, or both. The most common is Down syndrome [5], caused by an extra #21 chromosome.

Inherited Genetic Diseases

Examples are:

• Tay-Sachs disease [6]—most frequent in the Ashkenazi Jewish population
• Cystic fibrosis [7]—most common in Caucasians of northern European ancestry
• Sickle cell disease [8]—most frequent in the Black population

Test results for inherited genetic diseases are usually ready in 1-5 weeks.

Neural Tube Defects

The standard test measures a protein called alpha-fetoprotein (AFP). It detects over 99% of all open neural tube defects. The results are ready in one week or less.

Anesthesia

Local (optional)

Description of the Procedure

It is done in a doctor's office or hospital clinic, usually when a woman is about 16 weeks pregnant.

First, your doctor will do an ultrasound [10] scan (sonogram), to choose a safe spot for inserting the amniocentesis needle. Your abdomen is cleaned, and a very thin needle is inserted through your abdomen into your uterus. A few teaspoons of amniotic fluid are withdrawn.

After the needle is removed, the doctor will make sure that the fetal heartbeat is normal. In most cases, ultrasound imaging will be used throughout the procedure.

How Long Will It Take?

Locating the fetus and inserting the needle can take up to 20 minutes. Withdrawing the fluid takes five minutes. You will be asked to remain on the table for an additional 15 or 20 minutes to relax.

Will It Hurt?

Some women say that amniocentesis doesn’t hurt at all. Others feel cramping when the needle enters the uterus or pressure during the few minutes while the fluid is being withdrawn.

Possible Complications

Amniocentesis is a routine procedure. It is usually safe, but does have some risks:

• Miscarriage [11]—Average risk for miscarriage is less than 1 in 200. Early amniocentesis (before 15 weeks) may have a somewhat higher risk at less than 1 in 100.
• Bleeding, cramping, and leaking fluid from the vagina—Occurs in about 1% of women having amniocentesis. Does not usually result in a miscarriage. If you have these symptoms, call your doctor.
• Infection—Very rare. Great care is taken to prevent this.
• Harm to the fetus—The risk that the needle will touch the fetus is extremely low.
• Rh problems [12]—If you have Rh-negative blood type, and the baby's father has Rh-positive blood, you should have an injection of Rh immune [13] globulin after the procedure. This helps prevent Rh disease in the baby.
• Repeat testing—Very rare. The doctor may not obtain enough amniotic fluid, or the laboratory test cannot be done for some reason. Neither of these means that something is necessarily wrong with the pregnancy, but the amniocentesis will have to be repeated.

Deciding whether or not to have amniocentesis usually depends on your special risks, concerns, and family history.

Average Hospital Stay

None

Postoperative Care

• Rest for 24 hours after the procedure
• For the first few hours, avoid physical stress [14] such as lifting and prolonged standing
• Bathe and shower as usual
• No heavy exercise [15] or sexual relations for 24 hours