What Does Amniocentesis Test For?

Amniocentesis can be done to test for the following:

• Genetic testing: Testing the amniotic fluid can help diagnose genetic disorders such as Down syndrome, spina bifida, or cystic fibrosis. Amniocentesis to test for genetic abnormalities is usually performed in the second trimester after 15 weeks of pregnancy.
• Fetal lung maturity testing: Testing the maturity of the fetal lung can help determine whether a baby's lungs are mature enough for birth. Amniocentesis to determine the baby’s lung maturity is usually performed later in the course of pregnancy between 32 and 39 weeks.
• Diagnosis of fetal infections: Amniotic fluid testing can be done to evaluate the baby for infection or other illness.
• As a treatment procedure: Amniocentesis may be done as a treatment procedure for conditions such as polydraminos. Polyhydraminos is a condition in which there is an excess accumulation of the amniotic fluid during pregnancy. Amniocentesis may be done to drain excess amniotic fluid from the uterus.
• Paternity testing: Fetal cells in the amniotic fluid can be analyzed for DNA paternity testing.

Amniocentesis is highly indicated in the following cases:

• Positive results from a prenatal screening test indicate the possibility of abnormalities. Amniocentesis is done to confirm or rule out a diagnosis.
• Having another child with a genetic abnormality
• Babies born to women aged 35 years and older have a higher risk of chromosomal conditions such as Down syndrome. Your healthcare 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
• Abnormal ultrasound findings during routine examinations during pregnancy

Amniocentesis is usually not advised in the following cases:

• An active infection in the mother
• Human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS)
• Hepatitis B or C infections

Similarly, the above infections can be transmitted to the baby during amniocentesis.

During the procedure: The patient is made to lie on the back and an ultrasound is usually done prior to amniocentesis to determine the baby's exact location in the uterus. The abdomen is cleaned with an antiseptic. Anesthesia is usually not used, but most women experience mild or no discomfort during the procedure. A long and thin needle is inserted through the abdomen and into the uterus under ultrasound guidance. A small amount of amniotic fluid is aspirated into a syringe, and the needle is removed. The fluid is then sent to the lab for analysis.

After the procedure: The patient may be required to stay in the clinic or hospital for a few hours to monitor the baby’s vitals after the procedure. Some patients may experience mild cramping or pelvic discomfort, which usually resolves. Patients can resume normal activities after the procedure, but exercise and sexual activity should be avoided for two or three days.

Amniocentesis carries various risks including:

• Leaking amniotic fluid: Although rare, the amniotic fluid leaks through the vagina after amniocentesis, but usually, only a small amount is lost and stops within a week.
• Miscarriage: There is a small risk of miscarriage in second-trimester amniocentesis. The risk of miscarriage is higher following amniocentesis when it’s done before 15 weeks of pregnancy.
• Rh sensitization: During amniocentesis, the baby's blood cells may enter the mother's bloodstream. If there is an Rh-negative or Rh-positive blood group mismatch between the mother and baby, it can cause serious complications.
• Infection: Uterine infection can occur following amniocentesis.
• Infection transmission: Infections in the mother such as hepatitis B or C, toxoplasmosis, and sexually transmitted diseases can transmit to the baby during the procedure.
• Needle injury: Because the needle is long (but thin), it could injure the baby if they move an arm or a leg, but these injuries are rarely serious.