Amniocentesis is a procedure in which amniotic fluid is removed from the uterus for testing or treatment. Amniotic fluid is the fluid that surrounds and protects a baby during pregnancy. This fluid contains fetal cells and various chemicals produced by the baby. Amniocentesis can be done for various reasons:

  • With genetic amniocentesis, a sample of amniotic fluid is tested for certain conditions such as Down syndrome and Spina Bifida.
  • With maturity amniocentesis, a sample of amniotic fluid is tested to determine whether the baby’s lungs are mature enough for birth.
  • Occasionally, amniocentesis is used to evaluate a baby for infection or other illness.
  • Rarely, amniocentesis is used to decrease the volume of amniotic fluid.

Although amniocentesis can provide valuable information about your baby’s health, the decision to pursue invasive diagnostic testing is serious. It’s important to understand the risks of amniocentesis and be prepared for the results.

Amniocentesis is done for different reasons at different stages of pregnancy.
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. Typically, the value of this information can only be assessed by you and your partner.
Genetic amniocentesis is usually done after week 15 of pregnancy. Rarely, genetic amniocentesis might be done as early as week 11 of pregnancy.
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 noninvasive prenatal testing 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 Down syndrome or a neural tube defect a serious condition affecting the brain or spinal cord this pregnancy is at higher risk, too.
You’re 35 or older. Babies born to women 35 and older have a higher risk of chromosomal conditions, such as Down syndrome.
You have a family history of a specific genetic condition. In addition to identifying Down syndrome and spina bifida, amniocentesis can be used to diagnose many other conditions such as cystic fibrosis.
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. 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..

Other reasons for amniocentesis
Occasionally amniocentesis is used to:

Evaluate a baby for infection or other illness
Decrease the volume of amniotic fluid
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.

If you’re having amniocentesis done before week 20 of pregnancy, your bladder must be full during the procedure. Drink plenty of fluids before your appointment. After 20 weeks of pregnancy, your bladder must be empty during amniocentesis.

Amniocentesis is usually done in an outpatient facility or the health care provider’s office and takes about 20 to 30 minutes.
First, your health care provider will use ultrasound to determine the baby’s exact location in your uterus. Generally, anesthetic isn’t used. Guided by ultrasound, your health care provider will insert a thin, hollow needle through your abdominal wall and into the uterus. A small amount of amniotic fluid will be withdrawn into a syringe, and the needle will be removed. The specific amount of amniotic fluid withdrawn depends on the number of weeks the pregnancy has progressed.
You might notice a stinging sensation when the needle enters your skin, and you might feel cramping when the needle enters your uterus.

After the amniocentesis, your health care provider might use ultrasound to monitor your baby’s heart rate. You might experience cramping or a small amount of vaginal bleeding immediately after the amniocentesis. Avoid strenuous physical activity for a day or two. Meanwhile, the sample of amniotic fluid will be analyzed in a lab. Some results might be available within a few days. Other results might take up to four weeks. Contact your health care provider if you have: Persistent fluid leaking from your vagina Heavy vaginal bleeding Abdominal pain or uterine cramping that lasts more than a few hours Fever Redness and inflammation where the needle was inserted Unusual fetal activity or a lack of fetal movement

For genetic amniocentesis, test results can reliably rule out or diagnose various genetic conditions, such as Down syndrome. Amniocentesis can’t identify all birth defects, however.
For maturity amniocentesis, test results can reliably indicate a baby’s lung maturity. If you need to deliver the baby early, this information offers reassurance that your baby is ready for birth.