The watery fluid surrounding the fetus during pregnancy is called amniotic fluid. It is encased in the amniotic sac and keeps the baby warm and cushioned from the outside environment. It also contains valuable information about the baby’s health and development.
A prenatal test that takes amniotic fluid from around your baby in the uterus (also called womb) to determine baby’s health conditions is amniocentesis. A prenatal test is a medical procedure performed on pregnant women. Your OB-GYN can test the amniotic fluid with this procedure.
An amniocentesis can be performed during a prenatal appointment, usually between the 15th and 18th weeks of pregnancy. It involves withdrawing a small amount of amniotic fluid through a very thin needle inserted through the uterine and abdominal walls. The needle is carefully guided using ultrasound to avoid the developing fetus.
The sample of amniotic fluid sample is then sent to a lab for testing. Typically, the doctor will order specific tests depending on the rationale for the amniocentesis and the baby’s genetic risk for certain conditions.
Talk to your health care provider to see if amnio is right for you.
Amniocentesis is typically performed to test for certain birth defects and genetic conditions. Amniocentesis is a diagnostic test that detects chromosomal abnormalities, neural tube defects and genetic disorders with high levels of accuracy. The lab also can test the amniotic fluid for proteins like alpha-fetoprotein (also called AFP). AFP levels are often higher if your baby has a neural tube defect.
Usually, amniocentesis is only performed if there is a reason to suspect the baby is at risks, such as a family history of genetic diseases or advanced maternal age. Amniocentesis might be performed if the mother had a previous pregnancy with a birth defect or if an ultrasound exam showed abnormal results.
Like all genetic testing, amniocentesis is optional. It is generally offered when:
- Results of a screening test (the combined first-trimester bloodwork, the quad screen or noninvasive prenatal testing (NIPT)) turn out abnormal and you’ve missed the window for CVS (or opted not to get CVS because that test can’t detect neural tube defects). Because amnio is a diagnostic test, it can give a more accurate answer as to whether or not there actually is a fetal abnormality.
- You already have a child with a condition that can be diagnosed with the amnio, like Down syndrome or cystic fibrosis.
- You or your partner has a family history of a genetic condition like Tay-Sachs disease or sickle cell anemia
- Toxoplasmosis, fifth disease, cytomegalovirus or another fetal infection is suspected.
- You’re an older mom (usually meaning over 35) and want to rule out that your baby has Down syndrome since there’s a slightly higher risk of it in older moms.
- There’s a medical reason to deliver the baby a week or two early; amnio can show whether the baby’s lungs are mature enough to induce labor.
What Can an Amniocentesis Test For?
Amniocentesis can test for multiple conditions including:
- Down syndrome
- Cystic Fibrosis
- Sickle cell anemia
- Tay-Sachs disease
- Muscular dystrophy
- Spina bifida
Amniocentesis is also sometimes performed in the third trimester to check on the fetal lung maturity if early delivery is recommended. Aside from the baby’s lungs being checked the baby’s gender can also be confirmed. Test results are available within 2-3 weeks.
It does not, however, detect every kind of abnormality, including cleft lip or palate, and it can’t determine the severity of the problem.
Amniocentesis carries a small risk of miscarriage, which occurs in about 1 in 200-400 procedures. There is some risk of injury, infection, and preterm labor, but these complications are exceedingly rare.
Amniocentesis may be uncomfortable. Typically, a local anesthetic is administered to numb the area where the needle will be inserted. Even so, you may feel cramping and pain during and for a couple of hours after the procedure. It’s recommended that you go home after the procedure and rest. You should avoid exercise, sexual intercourse, and lifting anything heavier than 15 pounds.
Amnio may cause a small amount of your baby’s blood to mix with your blood. If you’re Rh-negative and your baby is Rh-positive, you may get a shot called Rh immune globulin after amnio to help protect your baby.
Rarely, amniotic fluid leaks through the vagina after amniocentesis. However, in most cases, the amount of fluid lost is small and stops within one week, and the pregnancy is likely to continue normally.
Second-trimester amniocentesis carries a slight risk of miscarriage.
If you develop a fever or experience vaginal bleeding, discharge, or severe pain during your recovery, please call your OB-GYN immediately. It may be a sign of infection or another complication.
Another related procedure that may be used to diagnose genetic and chromosomal defects is chorionic villus sampling. Some women prefer to have trimester screen or prenatal cell-free DNA screening, called a screening test, before making up their mind about having an invasive test like amniocentesis.
Ultimately, the decision to have genetic amniocentesis is up to you. Your health care provider or genetic counselor can help you weigh all the factors in the decision.