Amniocentesis can be done for various reasons:

  • Genetic testing. Genetic amniocentesis involves taking a sample of amniotic fluid and testing it for certain conditions, such as Down syndrome.
  • Fetal lung testing. Fetal lung maturity testing involves taking a sample of amniotic fluid and testing it to determine whether the baby's lungs are mature enough for birth.
  • Diagnosis of fetal infection. Occasionally, amniocentesis is used to evaluate a baby for infection or other illness. The procedure also can be done to evaluate the severity of anemia in babies who have Rh sensitization — an uncommon condition in which a mother's immune system produces antibodies against a specific protein on the surface of the baby's blood cells.
  • Treatment. If you accumulate too much amniotic fluid during pregnancy (polyhydramnios), amniocentesis might be done to drain excess amniotic fluid from your uterus.

Genetic amniocentesis

Genetic amniocentesis can provide information about your baby's genetic makeup. Generally, genetic amniocentesis is offered when the test results might have a significant impact on the management of the pregnancy or your desire to continue the pregnancy.

Genetic amniocentesis is usually done between week 15 and 20 of pregnancy. Amniocentesis done before week 15 of pregnancy has been associated with a higher rate of complications.

You might consider genetic amniocentesis if:

  • You had positive results from a prenatal screening test. If the results of a screening test — such as the first trimester screen or prenatal cell-free DNA screening — are positive or worrisome, you might opt for amniocentesis to confirm or rule out a diagnosis.
  • You had a chromosomal condition or a neural tube defect in a previous pregnancy. If a previous pregnancy was affected by conditions such as Down syndrome or a neural tube defect — a serious condition affecting the brain or spinal cord — your health care provider might suggest amniocentesis to confirm or rule out these disorders.
  • You're 35 or older. Babies born to women 35 and older have a higher risk of chromosomal conditions, such as Down syndrome. Your health care provider might suggest amniocentesis to rule out these conditions.
  • You have a family history of a specific genetic condition, or you or your partner is a known carrier of a genetic condition. In addition to identifying Down syndrome and spina bifida, amniocentesis can be used to diagnose many other conditions — such as cystic fibrosis.
  • You have abnormal ultrasound findings. Your health care provider might recommend amniocentesis to diagnose or rule out genetic conditions associated with abnormal ultrasound findings.

Fetal lung maturity amniocentesis

Fetal lung maturity amniocentesis can determine whether a baby's lungs are ready for birth. This type of amniocentesis is done only if early delivery — either through induction or C-section — is being considered to prevent pregnancy complications for the mother in a non-emergency situation. It's usually done between 32 and 39 weeks of pregnancy. Earlier than 32 weeks, a baby's lungs are unlikely to be fully developed.

Amniocentesis isn't appropriate for everyone, however. Your health care provider might discourage amniocentesis if you have an infection, such as HIV/AIDS, hepatitis B or hepatitis C. These infections can be transferred to your baby during amniocentesis.

Oct. 13, 2015