Amniocentesis
Who Should Consider Amniocentesis?
Amniocentesis should
generally be considered by women age 35 or older at the
time of delivery, individuals who have had a child with
a chromosome abnormality, individuals who have a chromosome
translocation or other rearrangement, couples at risk
for a prenatally diagnosable genetic disease (e.g., hemophilia,
sickle cell disease, or cystic fibrosis), and individuals
with a child or other close family members with a neural
tube defect (spina bifida or anencephaly). Amniocentesis
may also be considered when certain abnormalities are
seen on ultrasound or when maternal serum screening has
identified an increased risk for fetal anomalies.
How Is Amniocentesis Performed?
An ultrasound evaluation is performed to assess fetal development, to locate
the placenta, to determine fetal age, and to select a pocket of amniotic
fluid. A site is identified on the woman's abdomen and with ultrasound
guidance, a thin needle is inserted through the abdomen and into the uterus.
A small amount of amniotic fluid is removed and sent to be analyzed.
Does The Procedure Hurt?
Most women describe the procedure as mildly uncomfortable. Some women do experience
cramping after the test. Most women are able to return to normal activities
shortly after the test.
What Is The Risk of Miscarriage
After Amniocentesis?
The most common complications are vaginal spotting or bleeding, severe cramping,
or miscarriage. Maternal infection is rare. The procedure-related risk for
any complication, including miscarriage, is approximately 1 in 200.
What Is Analyzed From Amniocentesis?
Cells shed from the amnion (the sac surrounding the fetus), fetal skin, and
gastrointestinal tract are normally floating in the amniotic fluid. These
cells can be grown (cultured) in the laboratory. Chromosome analysis is performed
on these cultured cells. AFP (alpha-fetoprotein) is also present in the amniotic
fluid and is measured.
What Can Be Detected Through Amniocentesis?
Chromosome abnormalities (such as Down syndrome) can be detected through amniocentesis.
The majority of neural tube defects are detected by elevated levels of AFP
in the amniotic fluid. Some specific genetic disease can be diagnosed by
DNA or enzyme analysis if indicated.
No method of prenatal testing can guarantee
a baby will be born without birth defects or genetic
disease. Prenatal testing can only identify the diagnosable
problems for which a couple is known to be at risk. Unfortunately,
there are many conditions for which prenatal diagnosis
is not yet available.
How Accurate Are The Results from
Amniocentesis?
Chromosome results are greater than 99% accurate. Measurement of the amniotic
fluid AFP is greater than 96% accurate in detecting neural tube defects. Occasionally,
results need to be clarified through blood tests on the parents, ultrasound,
a repeat amniocentesis, or fetal blood sampling.
How Long Do The Results Take?
Chromosome and amniotic fluid AFP results take
approximately 2 weeks for completion. Special studies
for other genetic diseases may take longer. Patients
who elect to have an aneuploidy FISH test on their
sample can receive those results in 24-48 hours from
the day of the procedure.
