Amniocentesis is a procedure used to test for birth defects. It
involves obtaining a sample of
amniotic fluid
(fluid in the
amniotic sac
that surrounds the fetus) from which cells of
the fetus can be tested. It can detect chromosomal problems such as
Down syndrome
, or genetic diseases such as
cystic
fibrosis
,
Tay-Sach's disease
, and
sickle cell
disease
. It can also detect the sex of the fetus.
Your health care provider will make recommendations for testing
based on your genetic risk. Testing should be recommended if:
- You will be 35 years old or older when you give birth.
- You have a family history of certain birth defects.
- You already had a child with a birth defect.
- You have abnormal results on other genetic tests.
Amniocentesis is usually done in the 15th to 18th week of
pregnancy. The procedure is performed in the health care provider's
office or hospital and does not require an overnight stay. You will
lay down with your abdomen uncovered. You will then be given an
ultrasound. The ultrasound helps the clinician will know where to
insert the needle that will be used to withdraw the sample of
amniotic fluid. The needle will then be carefully placed through
the your abdomen and uterus and into the amniotic sac. If you are
carrying twins, you will need to have fluid withdrawn from each
amniotic sac. About 1 ounce of fluid is withdrawn and then sent to
the lab so that the cells can be tested. Results may take about two
weeks.
Other tests for birth defects can be performed using the
amniotic fluid, including the
alpha-fetoprotein (AFP) test
.
AFP is a protein produced by the fetus, which passes into the
amniotic fluid. Too much AFP can be a sign of open neural tube
defects or openings in the abdomen of the fetus. AFP can also be
checked with a blood test.
Amniocentesis tends to be a fairly safe procedure for the mother
and her fetus. However, complications occur in a minority of cases
and may include:
- Cramping, bleeding, or infection
- Leaking of amniotic fluid
- Miscarriage (in less than 1 out of every 200 women who have the
test)
