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Genetic
Amniocentesis
Introduction
Amniocentesis is a safe and effective procedure for prenatal diagnosis
of birth defects and genetic disorders. GLG was the first independent
genetic clinic for prenatal diagnostic testing in Wisconsin and
continues to be the prenatal diagnostic consultant of choice for
many obstetricians and family physicians. GLG physicians combine
the resources of substantial experience (over 10,000 amniocentesis
procedures) with an outstanding safety record.
Unlike most other prenatal
diagnostic centers, GLG provides amniocentesis as a fully integrated
combination of clinical and laboratory services. The intake counseling
with review of the patient's family and past medical histories,
and a comprehensive discussion of the procedure, are conducted by
the physician geneticist who will examine the baby by ultrasound
and perform the amniocentesis. These tasks are not delegated to
technicians, counselors, or other support personnel.
The studies on the amniotic
fluid and cells are carried out in the in-house GLG laboratory.
The doctor performing the ultrasound examination and amniocentesis
can review and interpret the laboratory results directly. This integrated
approach is particularly helpful when results are abnormal. When
circumstances arise that require further discussion or examination,
the follow-up is conducted by the same genetic doctor who initially
saw the patient.
At GLG, the amniocentesis
procedure is always preceded by a detailed ultrasound examination
of the baby in order to rule out nonchromosomal birth defects and
other disorders. The combination of a detailed ultrasound examination
with an amniocentesis rules out the presence of about 70% of genetic
disorders and birth defects. This includes Down syndrome and other
chromosome disorders, as well as most major congenital malformations.
It will rule out all cases of spina bifida.
Description
Amniocentesis is performed to obtain amniotic fluid and fetal cells
for prenatal diagnostic testing. Amniotic fluid cells are cultured
and analyzed to determine the fetal chromosome constitution. The
cells can also be used for biochemical or molecular studies, if
indicated. Usually the amount of AFP in the amniotic fluid is measured.
In certain cases the presence or absence of acetylcholinesterase
in the amniotic fluid is also determined. Typically, amniocentesis
at GLG is performed after 14 weeks gestation.
Procedure
Amniocentesis involves aspiration of 15 cc of amniotic fluid from
the amniotic sac, using sterile technique and an ultrasound needle
guide. The guide shows the path the needle will take and allows
continuous observation of the needle during the procedure. Amniocentesis
takes about 30 seconds. To the patient, amniocentesis feels similar
to having blood drawn. There are no special precautions necessary
before or after the procedure, and it is not necessary for the patient
to have a full bladder.
Indications
The most common indications include:
• advanced maternal age
• abnormal prenatal ultrasound findings
• abnormal maternal serum screen results
• previous child with a chromosome abnormality
• familial chromosome rearrangement
• biochemical or molecular diagnosis of a familial genetic disorder
Risks
In the experienced hands of the physician geneticists at GLG there
is an approximate 1/1000 risk of miscarriage from amniocentesis.
There is also an approximate 1/200 risk of the procedure causing
a leak of arnniotic fluid, which would require bed rest for the
amniotic sac to seal; this has never caused a problem for the baby.
Turn Around
Time
The fetal karyotype is usually available after eight days. Amniotic
fluid AFP results take 1-2 days and ACHE results are usually available
in 4-5 days. Many molecular genetic tests are performed directly
from the fetal cells without prior tissue culture, which means the
results can be available within a few days. Both the patient and
referring doctor are promptly notified that the results are available,
and the doctor receives a detailed report. Usually it is not necessary
for the patient to return to GLG for follow-up.
CPT Codes
99244 - consultation,
level 4
59000 - amniocentesis
76946 - ultrasound guide, amniocentesis
76805 - ultrasound examination, complete
88269 - chromosome analysis, amniotic fluid
88235 - tissue culture for amniotic fluid
88244 - amniotic fluid alpha-fetoprotein
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