Amniocentesis

March 2, 2010

Determining Diagnostic Testing: Amniocentesis

Pregnancy is a time fraught with various anxieties, especially if the pregnancy is the first. So many changes in the body, and so many new and strange feelings make it exciting and tense all at the same time. For some women, the tension is increased because they have a higher risk for having a baby with a genetic abnormality or disorder. A previous pregnancy with a child that had a genetic abnormality or a family history of chromosomal abnormalities or genetic disorders can put a child at greater risk for problems. Also, a woman who is older has a higher risk of producing a baby with genetic or chromosomal abnormalities.

Before any diagnostic testing is done, a visit to a genetic counselor is wise. In a visit with a counselor the risks and benefits of the various prenatal screenings and tests can be discussed and evaluated. If the answers to the questions asked by the counselor indicate there is a risk for having a baby with chromosomal or genetic problems, then a decision as to whether or not testing will be done can be made.

What Is Amniocentesis And Why Do I Need One?

One type of testing that evolves from genetic counseling is amniocentesis which is the taking of a sample of amniotic fluid from the womb. The amniotic fluid surrounds the baby in the uterus. This type of testing is most frequently done to determine if there is a genetic or chromosomal disorder in the baby, such as Down syndrome. The other test that can determine such disorders is a chorionic villus sampling (CVS). The amniocentesis is usually done when the woman is between 16 and 20 weeks gestation. This test is invasive and does carry a risk of miscarriage.

Other reasons for having an amniocentesis include determining if the baby's lungs are mature enough to withstand an early delivery if the mother appears to need to deliver early. It can be used to rule out an infection if the amniotic sac ruptures early. It is also used to check on the well-being of the baby in the event of blood sensitization, such as is the case with Rh sensitization. Today, doctors are using Doppler ultrasound instead of amniocentesis to diagnose and address the Rh concerns.

Detecting Chromonsomal Abnormalities 

Amniocentesis is able to detect many different chromosomal disorders, including Down syndrome, trisomy 13, trisomy 18, Turner syndrome and Klinefelter syndrome. Amniocentesis has shown to be accurate in 99 percent of diagnoses. There are other disorders that can be detected by amniocentesis, especially genetic disorders like cystic fibrosis, sickle cell anemia, and Tay-Sachs disease. It is also effective in determining defects such as spina bifida and anencephaly. Heart malformations, cleft lip or palate are beyond the abilities of this testing. However, there are structural defects that can be noted in the second-trimester ultrasound that is standard practice for any woman who has had an amniocentesis.

If, after the amniocentesis is completed, the findings indicate there is a problem, genetic counseling is offered in order to help with options and the decisions that face the mother and/or couple. Some women opt to abort while others decide to carry on and do whatever comes next. Whatever the decision, counseling and support is offered to help during this time of decision.

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