The sample of fluid is analyzed in the lab. Amniotic fluid contains cells from the baby. Early in pregnancy the cells can be tested for certain genetic problems the baby might have. Amniocentesis is sometimes done near the end of a pregnancy to test the maturity of a baby's lungs. When the test is done for genetic screening, it is usually done between the 15th and 18th weeks of pregnancy.
Prenatal tests show an increased likelihood of a problem with the baby.
You have given birth to a child with Down syndrome or another genetic disorder. You or your baby's father have a family history of genetic problems. You have a child with a defect in the spinal cord or brain. You have had three or more miscarriages. Amniocentesis may be done later in pregnancy to see if the baby's lungs are mature enough for the baby to breathe well after birth.