Amniocentesis

Amniocentesis is a test to look at the fluid (Reference amniotic fluid Opens New Window) that surrounds your Reference baby (fetus) Opens New Window. 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 Reference uterus Opens New Window. About 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 doing.

Amniocentesis for birth defects testing

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.

Amniotic fluid has cells that have been shed by your developing fetus. The cells are checked for the number and size of Reference chromosomes Opens New Window (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 Reference cleft lip Opens New Window, Reference cleft palate Opens New Window, heart problems, and some types of intellectual disability.

Opens New Window Pregnancy: Should I Have Amniocentesis? Opens New Window

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.

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