Amniocentesis is a test to look at the fluid (amniotic fluid) that surrounds your
baby (fetus). Amniotic fluid has cells and other
substances that can give clues about the health of your fetus. Amniocentesis is
done by gently putting a needle through your belly into your
2 Tbsp (30 mL) of the amniotic
fluid is taken out and looked at.
Amniocentesis is generally done
between weeks 15 and 20 (usually around week 16) to look at genetic
information. It can also be used later in pregnancy to see how the fetus is
Amniocentesis is offered to women who would like a test to
find problems with the fetus. These include women:
- With a close family member who has a genetic
- Who have an abnormal screening test for birth defects in the
- Who have an abnormal triple or quadruple screen
test (alpha-fetoprotein, estriol, human chorionic gonadotropin, hormone inhibin
- Who have a
fetal ultrasound that shows problems, such as a heart
problem or too much amniotic fluid.
Amniocentesis is often done around
week 16 to see whether a fetus has certain types of birth defects.
Amniocentesis can also tell the sex of your fetus.
has cells that have been shed by your developing fetus. The cells are checked
for the number and size of
chromosomes (karyotype) to see if there are any
problems that put the baby at risk for certain conditions. Testing is most
commonly done as early as possible so that women and their families have time
to consider their options. But amniocentesis cannot find many common birth
defects, such as
cleft palate, heart problems, and some types of intellectual disability.
Amniocentesis is not done as a general screening
test for birth defects, because it has an increased risk to your fetus. One
study showed the chance of
miscarriage from amniocentesis was small (about 1 out of
400) when it is done by highly trained providers.1 In
some studies, the risk is a little higher, about 2 to 4 out of 400.2 Amniocentesis can be done to help you prepare if your fetus
has a possible birth defect or to help you make a decision about ending the
pregnancy if a serious problem is found.
Pregnancy: Should I Have Amniocentesis?
Amniocentesis in late pregnancy
If you are at risk
of having your baby early, amniocentesis may be done during the third trimester
to see whether your baby's lungs are developed. Your developing fetus makes
substances that can be found and measured in amniotic fluid. The amounts of
these substances show how mature the lungs are and if your baby will be able to
breathe without help if delivered early.
Amniocentesis may also be
done later in pregnancy if an infection of the amniotic fluid
(chorioamnionitis) is suspected.