AMNIOCENTESIS PRENATAL TEST FOR PREGNANCY
Amniocentesis is a common prenatal test in which a small sample of the amniotic
fluid surrounding the fetus is removed and examined. The technique was first
used in 1882 to remove excess amniotic fluid (1). Today, amniocentesis often
is used to diagnose or, far more likely, rule out certain birth defects.
What is Amniocentesis?
Amniocentesis test is carried out on a pregnant woman to collect information
about the fetus from a sample of the amniotic fluid. The fetus is surrounded
by the amniotic fluid inside the uterus. Amniocentesis is not advised for ever
pregnancy women because it carries a small risk of miscarriage. This Amniocentesis
test only recommended when there is increased the risk of chromosomal or genetic
birth defects or certain malformations. Amniocentesis test is usually performed
in the second trimester or anywhere between 11 – 14 weeks of pregnancy.
Some recommended risk that pregnant woman should be take Amniocentesis test
:
- Maternal age. The risk of bearing children with certain
chromosomal birth defects increases as a woman ages. If a woman will be 35
or older at the time of delivery, health care providers offer the option of
prenatal diagnostic testing for chromosomal disorders. The most common of
these disorders is Down syndrome, a combination of mental and physical abnormalities
caused by an extra chromosome. Down syndrome occurs in about 1 in 1,250 children
born to women in their 20s. The chances increase to about 1 in 400 by age
35, 1 in 100 at age 40, and 1 in 30 at age 45 (2).
- A previous child or pregnancy with a birth defect. If a
couple already has had a child (or pregnancy) diagnosed with a chromosomal
abnormality, a genetic birth defect, or certain birth defects involving the
brain or spinal cord (neural tube defects or NTDs), the couple may be offered
prenatal testing during subsequent pregnancies.
- Family history. Couples with a family history of certain
birth defects, such as cystic fibrosis (lung disease) or fragile X syndrome
(mental retardation), may be offered amniocentesis.
- Abnormal screening test results. Screening tests for birth
defects can be done in the first or second trimester. The first-trimester
screening test combines a blood test with an ultrasound exam to measure the
skin fold at the back of the fetal neck. The second trimester screening test
also can suggest an increased risk for neural tube defects. Abnormal results
on either the first- or second-trimester screening test can suggest an increased
risk of Down syndrome and certain other chromosomal abnormalities. Amniocentesis
can diagnose or rule out chromosomal abnormalities and can help diagnose NTDs.
Most chromosomal disorders such as Down syndrome and Edward’s syndrome
can be detected with the help of an amniocentesis test. It is also possible
to diagnose conditions such as cystic fibrosis, sickle cell disease, Huntington’s
disease and Tay-Sachs disease. Neural tube defects such as spina bifida and
anencephaly can be detected with an amniocentesis test. However, no one prenatal
test can guarantee the birth of a healthy baby, since only some birth defects
can be ruled out before birth. Amniocentesis test has an accuracy rate of between
99.4 and 100 % in diagnosing chromosomal abnormalities.
Other reasons for suggesting an amniocentesis test:
- To determine whether the fetal lungs are mature for early delivery, in
case circumstances demand it
- An amniocentesis test can diagnose uterine infections
- Amniocentesis can help in determining the severity of fetal anemia in cases
of Rh disease
How is Amniocentesis Test?
This procedure takes about 20 minutes. The technician uses an ultrasound to
detect a pocket of amniotic fluid that is a safe distance from the baby and
placenta. A long, thin and hollow needle is inserted through the abdominal wall
into the amniotic fluid. A small amount of amniotic fluid is drawn out for testing.
While some women experience cramping or pinching, others feel no discomfort
at all. It is advisable to take it easy for a day and avoid heavy work.
Some women notice spotting or leaking amniotic fluid. After the sample is taken,
the physician uses ultrasound to check that the fetal heartbeat is normal. The
amniotic fluid drawn during the test is tested in a laboratory for chromosomal
abnormalities and genetic birth defects. The amniotic fluid contains numerous
free-floating fetal cells that can be grown in a laboratory. When these cells
multiply and reach a certain number, their chromosomes or genes are extracted
and analyzed. It takes nearly 3 weeks to procure the results from an amniocentesis
test.
When is Amniocentesis Done?
Amniocentesis usually is done in the second trimester between 15 and 20 weeks
of pregnancy. Some medical centers offer early amniocentesis, done in the first
trimester, between 11 and 14 weeks after the last menstrual period. However,
recent studies suggest that early amniocentesis is riskier than second-trimester
amniocentesis.
What is The Risk of Amniocentesis?
According to the Centers for Disease Control and Prevention (CDC), the rate
of miscarriage with amniocentesis is between one in 400 and one in 200 procedures.
First-trimester amniocentesis carries more risk than second-trimester amniocentesis.
There is a slight risk of developing an uterine infection in the days following
the procedure. It is therefore essential to get the amniocentesis test done
under an experienced doctor. Knowing about your child’s condition can
help you prepare for challenges that you may have to face. With continuous ultrasound
guidance is used, injuries to the baby from the amniocentesis needle are very
rare. The amniocentesis needle is guided into the sac with the help of ultrasound
imaging. Once the needle is in the sac, a syringe is used to withdraw the clear
amber-colored amniotic fluid. The volume of fluid withdrawn depends upon the
age of the fetus and the reason for the testing.
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