Amniocentesis is a test to study the liquid (amniotic fluid)
that surrounds a baby. Amniotic fluid contains cells and other substances that
can give clues about a baby's health. Amniocentesis can be done after about the
15th week of pregnancy, when there is enough amniotic fluid for testing.
Amniocentesis is done by putting a needle through the belly into the
uterus. About 2 Tbsp (30 mL) of the amniotic fluid is collected and examined in
a lab. The fluid sample can be examined for:
Genetic characteristics, such as the sex of the
Chromosome problems, such as Down syndrome and some other
Chemicals that show how mature the baby's lungs are.
Levels of certain substances in the fluid sample, such as
alpha-fetoprotein, can also be checked. Some abnormal levels may mean there is
a problem with the development of the brain and nerves.
Amniocentesis is usually done between weeks 15 and 20 of the pregnancy
for genetic testing. It can be done later, during the third trimester of
pregnancy, to find out how mature the baby's lungs are.
Sarah Marshall, MD - Family Medicine & Siobhan M. Dolan, MD, MPH - Reproductive Genetics
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