AMNIOCENTESIS

Amniocentesis for genetic studies is usually performed between 16-18 weeks from the first day of the last menstrual period. Prior to the procedure, an ultrasound study (sonogram) is done to locate a pocket of fluid in the amniotic sac.  A thin sterile needle is inserted through the mother’s abdominal wall into the amniotic sac to withdraw a small sample (about 20cc, or 1½ tablespoons) of amniotic fluid. The fetus soon produces more fluid to replace the fluid withdrawn. Women may experience mild discomfort during the procedure.

The amniotic fluid contains cells that have been shed by the fetus and can be grown in the laboratory.  Several types of disorders can be detected by amniocentesis:

• chromosomal disorders (Down syndrome is the most common of these).
• open neural tube defects, such as spina bifida.
• certain genetic disorders such as cystic fibrosis, sickle cell anemia, and Tay-Sachs disease , if these tests are specifically ordered

If the mother is Rh negative and the father is Rh positive, the mother will receive an Rh immune globulin (RhoGAM) injection after the procedure to prevent Rh antibodies from forming.

Results of amniocentesis are generally available within two weeks.

Limitations:  Although amniocentesis can detect greater than 99% of the identifiable chromosomal abnormalities and 98% of neural tube defects, there can be no guarantee of a perfect baby.  Amniocentesis cannot detect all causes of birth defects, genetic disease, and/or mental retardation.  There is a very small chance that the cell growth will not be satisfactory, in which case a second amniocentesis would be needed.

Risk:  The risk of a miscarriage following amniocentesis is approximately 1 in 300. The cause(s) for miscarriage could be infection or a ruptured sac.

Aftercare:  It is recommended that physical activity be limited for 24 hours following the procedure.  Avoid:

heavy lifting (greater than 10 pounds)

• exercise
• sexual activity
• standing for long periods of time
• physically strenuous activities

Call your obstetrician immediately if you experience

• bleeding or leaking fluid from the vagina
• severe cramping (mild cramping, like menstrual cramps, is normal on the day of the procedure)
• signs of infection, such as fever or chills
  
  
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