female doctor performing amniocentesis on pregnant woman

Amniocentesis: what you need to know

An amniocentesis is a form of second trimester fetal diagnostic testing that can detect the presence of genetic and neural tube conditions, like Down syndrome, spina bifida, or Tay-Sachs. Performed by extracting and examining a bit of amniotic fluid for signs of these disorders, an amniocentesis is considered among the most conclusive methods of fetal testing.

When can I get amniocentesis?

Amniocentesis is available between weeks 15 and 20, though it is usually performed sometime between weeks 15 and 18. Amniocentesis can also be used in later pregnancy to check on, or in rare cases drain, the amniotic fluid.

How is an amniocentesis performed?

Once you arrive at your health care professionals’ office for your amniocentesis, he or she will begin by giving you an ultrasound to determine baby’s position, and to understand the levels of amniotic fluid that they will be dealing with. Your health care professional will then sterilize your abdomen and a needle, before (still guided by the ultrasound) inserting the needle, and extracting a small quantity of amniotic fluid.

Your sample will then be examined at lab, and returned to you usually within a few days to a week.

What are the risks of an amniocentesis?

Although an amniocentesis is safe in over 99% of instances, there is still a slight risk of injury, including a chance of infection or miscarriage. Miscarriage is of course the most serious risk of an amniocentesis, with research suggesting that the procedure will result in fetal death once out of every 300 to 500 procedures, although the real rate of occurrence may be slightly less.

Who should get an amniocentesis?

Because of the small but very real risk of fetal injury or miscarriage due to an amniocentesis, most doctors suggest only offerring them to certain pregnant women with particular risk factors for babies with genetic or developmental disorders. These risk factors include: 

  • Women over 35: Pregnant women over 35 have a heightened risk for having a baby with a chromosomal disorder like Down syndrome, or Edwards Syndrome, so most doctors will offer an amniocentesis to women over 35, though not all women over 35 will get them
  • Family history of genetic disorders: If there is a family history of a specific disease, or you know that you or your partner are carriers of a disease, it may be a smart move to undergo an amniocentesis
  • A previous screening test came up positive: If a previous test, like the First Trimester Combined Screen, Triple Screen, or Quad Screen came back positive, your health care provider will have you take an amniocentesis to confirm or deny the screening test’s result, provided there is a genetic linkage. It’s important to remember however, that because of the relatively high false positive rate of screening tests, and the relatively low prevalence of genetic conditions, the majority of women who have to take an amniocentesis because of a positive screen will not end up having an affected baby.

What diseases or disorders can an amniocentesis detect?

  • Aneuploidy (abnormal number of chromosomes) disorders like Trisomy 21 (Down syndrome), Trisomy 18 (Edwards Syndrome), and Trisomy 13 (Patau syndrome)
  • Neural tube defects like anencephaly or spina bifida
  • Other genetic diseases like Tay-Sachs, Cystic Fibrosis, or thalassemia

Another important consideration in your decision making process is cost. Where you go to get your test or procedure can make a tremendous difference in how much you pay.  It is common for costs to vary as much as 300- 500% for the same procedure depending on where you receive your treatment.  Amniocentesis can run anywhere between $150 and $300. To make sure you’re paying a fair price (the price you should reasonably pay) for your testing, check out Ovia’s price transparency partner Healthcare Bluebook. Their free pricing tool helps patients make smarter and more informed decisions about important medical procedures.

Find fair prices

Read more
  • Mayo Clinic Staff. "Second trimester pregnancy: What to expect." Mayo Clinic. Mayo Clinic, 5/15/2014. Web.
  • "ACOG's Screening Guidelines on Chromosomal Abnormalities." ACOG. American College of Obstetricians and Gynecologists, 5/7/2007. Web.
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