Amniocentesis

Amniocentesis is an optional prenatal test that can reveal important information about your baby before he or she is born. It is often performed during the second trimester of pregnancy (usually between 15 and 20 weeks) to test for some of the most common chromosomal and genetic birth defects, including Down Syndrome, cystic fibrosis, sickle cell disease, Tay-Sachs, Huntington’s disease, spina bifida and anencephaly. It can also be used later in pregnancy to assess anemia in babies with Rh disease, to determine if your baby’s lungs are mature enough for early delivery if you are experiencing preterm labor or must deliver early for another reason, and to determine whether you have an infection (if your water has broken early) or if your doctor suspects you may have one.

When testing for birth defects, amniocentesis is usually only offered to women who have certain risk factors, including:

• If they will be 35 years or older on their due date.
• Another test – such as a multiple marker screen, a nuchal fold scan, or CVS – indicated the baby is at a higher risk for a problem.
• They have previously been pregnant with a child with a birth defect.
• They have or the baby’s father has a chromosomal abnormality or genetic disorder or a family history that increases the risk that the child will have one too.

Before you have an amniocentesis, you should discuss with a genetic counselor all the risks and benefits associated with the test. While the incidence of problems resulting from an amniocentesis is rare, miscarriage does occur in approximately one in 200 to 400 cases, and there is a slight risk of uterine infection (less than one in 1,000) that can sometimes lead to miscarriage.

If you decide to have an amniocentesis, your doctor will first do an ultrasound to measure your baby and locate a pocket of amniotic fluid that is safely away from your baby. He or she will clean your abdomen with alcohol and then, under constant ultrasound monitoring, will insert a long hollow needle through your abdomen and into your amniotic sac and withdraw an ounce or two of amniotic fluid. You may feel a slight pinching, pressure, or cramping during the procedure, although some women feel nothing at all.

Afterwards, your doctor will check your baby’s heartbeat to ensure everything is normal. You should take it easy for the rest of the day and avoid strenuous activity for the next two days. You may continue to experience mild cramping, which is normal; however, if you have significant cramping, vaginal spotting or bleeding, develop a fever, or if you begin leaking amniotic fluid, contact your doctor immediately as these may be signs of infection or impending miscarriage.

The amniotic fluid is analyzed in the lab for the amount of alpha-fetoprotein (AFP) in the fluid, which can indicate neural tube defects such as spina bifida or anencephaly. Some of the baby’s cells are also allowed to grow in the lab for a week or two and then tested for chromosomal abnormalities and genetic birth defects. Results are usually available in two weeks. Amniocentesis has an accuracy rate greater than 99 percent in diagnosing chromosomal abnormalities.

Amniocentesis and CVS test for most of the same disorders, although CVS cannot diagnose neural tube defects. The procedures also have different levels of risk, timing, reliability and waiting time for results.

Even if you would never consider terminating your pregnancy if your baby were shown to have a chromosomal or genetic birth defect, finding out before birth can help you and your partner prepare emotionally. You may also choose to switch to a hospital that is better equipped to care for your baby, and your delivery team can also prepare for your baby’s birth and any procedures that may need to be done. Certain disorders can even be treated before birth, such as biotin dependence and MMA (methylmalonic academia) which are both extremely rare, but life-threatening if left untreated.

Some insurance plans cover amniocentesis and other prenatal tests, especially for women over 35 years of age. You may need a referral from your doctor or pre-authorization from your health plan for your health insurance to cover the procedure. The cost to the patient or insurance company averages about $1500; however, the price varies in different areas.

The decision to have an amniocentesis is a personal one that must be made after all the options, risks and benefits have been considered. Talk to your doctor and a genetic counselor to determine what is best for you and your baby.

For more information:

• AFP Test
• Nuchal Translucency Test
• Chorionic Villus Sampling
• Genetically Related Birth Defects
• Chat with other moms who are raising Children with Special Needs
• Chat with other women who are experiencing a High Risk Pregnancy