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Amniocentesis & Amniotic-Fluid Analysis
Amniocentesis & Amniotic-Fluid Analysis
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Amniocentesis & Amniotic-Fluid Analysis
Category: Reproductive system.
Subcategory: Tissue analyses.
Material studied: Amniotic fluid.
Estimated cost of test: $42.50 for lab work only. Does not include doctor's fee or cost of hospital or surgery facility.
Patient time for test: 45-60 minutes.
Reliability of test results: Good.
Available as home self-test? No.
Note: Test detects genetic characteristics and abnormalities before fetus is born. Procedure is frequently recommended for women over 35, for those who have had previous miscarriages or when there is a family history of genetic or chromosomal defects. In addition to genetic screening in early pregnancy, amniocentesis can be used to manage a problem pregnancy. Unfortunately, only 10% of about 400 birth defects can be detected by amniocentesis. Many birth defects such as congenital heart disease, cleft lip and palate, and certain types of mental retardation cannot be diagnosed by the test.
BEFORE THE TEST
Purpose of test:
Detects fetal abnormalities, particularly chromosomal characteristics and abnormalities, and disorders in fetal development of the nervous system.
Detects hemolytic disease* of newborn.
Determines maturity of fetus, especially the lungs.
Identifies sex of fetus, when one or both parents are carriers of a sex-linked disorder, such as hemophilia*.
Diagnoses metabolic disorders, amino-acid disorders, mucopolysaccharidosis*.
Assesses fetal health by detecting presence of feces or blood or measuring levels of estriol and fetal-thyroid hormone.
Where is test performed?
Free standing surgical clinic, hospital, doctor's office.
Who performs test?
Doctor.
Risks and precautions:
Tests are usually not valid until about the 16th week of pregnancy. Adverse effects are rare but include spontaneous abortion, injury to fetus or placenta, bleeding, premature labor and infection.
During the procedure, you are asked to fold your hands behind your head to prevent you from accidentally touching the sterile field and causing contamination.
Patient preparation:
Activity--No changes necessary.
Diet--Don't eat any food or drink any liquid for at least 12 hours before the test.
Medicines--No changes necessary.
Disrobing--Remove clothing. Put on surgical gown.
THE TEST
Sensory factors:
Touching--You will feel a stinging sensation when the local anesthetic is injected into the skin over the abdomen.
Seeing--You will see the technician, nurse or doctor, the basket or tray to hold the equipment, the needles, syringes, collecting tubes and bandages.
Feeling--Some degree of apprehension or fear is normal and should be expected. Discomfort disappears when the test is finished.
Other senses (smell, taste, hearing)--Not affected.
Equipment used:
Alcohol or povidone-iodine solution.
Sponge forceps.
Gauze pads.
Local anesthetic.
Sterile needle with syringe.
Sterile spinal needle with stylet.
Syringe.
Test tube.
Description of test:
You or a close relative will be required to sign a consent form after the procedure has been explained to you.
Fold hands behind your head.
The anesthetic is administered. The procedure does not begin until you are numb.
Skin is cleaned with antiseptic.
Position of the fetus is determined by ultrasonography.
Sterile spinal needle is inserted through skin, muscle and uterus into the amniotic cavity. It is aimed toward the back of the neck of the fetus.
Amniotic fluid (usually about 10ml) is suctioned through the needle into a collecting syringe.
Needle is withdrawn.
Small bandage is placed over the injection-withdrawal site on the skin.
Amniotic fluid is sent to the laboratory for analysis.
AFTER THE TEST
Immediate post-test care:
Your breathing rate, blood pressure and pulse, and the heart rate of the fetus are monitored every 15 minutes for at least 60 minutes.
Activity after test:
If you feel faint or nauseated or perspire profusely, lie on your left side to counteract uterine pressure.
If you experience abdominal pain or cramping, chills, fever, vaginal bleeding or leakage of vaginal fluid, fetal hyperactivity or unusual fetal lethargy, notify your doctor immediately!
Abnormal test results or failure of tissue cultures to grow may require repetition of the test.
Time before test results available: Several weeks.
TEST RESULTS
Test values:
Test results are determined by visual examination and chemical analysis.
Normal values:
Clear fluid with normal chromosomes and no bilirubin, meconium, bacteria or acetylcholinesterase.
More than 2mg/100ml of creatinine.
L/S ratio* greater than 2.
Phosphatidylglycerol present.
Glucose less than 45mg/100ml.
What ABNORMAL may indicate:
See Appendix 15.
Taking these drugs may affect test results:
None expected.
Other factors that may affect test results:
Infectious mononucleosis* of mother-to-be.
Cirrhosis* of mother-to-be.
Liver cancer of mother-to-be.
Teratoma* of mother-to-be.
Endodermal sinus tumor* of mother-to-be.
Gastric carcinoma* of mother-to-be.
Pancreatic carcinoma* of mother-to-be.
Subacute hereditary tyrosinemia* of mother-to-be.
Fetal blood in the fluid specimen.
Fetal feces in the fluid specimen.
Failure to fast overnight.
*See Glossary.
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From Complete Guide to Medical Tests by H. Winter Griffith, M.D. Copyright by Fisher Books. Electronic rights by Medical Data Exchange.
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