Amniocentesis is a prenatal test that allows you and your practitioner to gather information about your baby's chromosomes (genetics), from a sample of your amniotic fluid. The test removes a small amount of fluid from the sac around the baby to look for birth defects, lung maturity and chromosome problems.

The test is most commonly done when a woman is between 15 and 18 weeks pregnant to determine whether the baby has genetic or chromosomal abnormalities, such as Down syndrome, however can be done after 18 weeks.

What birth defects can the test detect?

Amniocentesis can identify several hundred genetic disorders, including some of the most common:

- Nearly all chromosomal disorders, including Down syndrome and Edward's syndrome. The test is more than 99 percent accurate in diagnosing these conditions. The multiple marker and ultrasound may indicate whether your baby is likely to have these problems, but only amniocentesis can tell you for sure.
- Other genetic disorders such as cystic fibrosis, Sickle cell disease, Tay-Sachs disease, or Huntington's disease. Neither the multiple marker nor ultrasound will pick up these problems. Only amniocentesis can provide the information needed to diagnose them in the womb.
- Neural tube defects such as spina bifida and anencephaly . If your amnio indicates that your baby is at risk for these problems, you'll have a detailed follow-up ultrasound for a diagnosis.

Is this test appropriate for me?

Although most centers will do an amnio for any pregnant woman who wants one, this procedure is not offered routinely to all pregnant women because it carries a small risk of miscarriage. It's usually only offered to those who are found to have a somewhat increased risk of having a baby with a chromosomal or genetic defect. You may be in this category if:

- You're going to be 35 years old or older when your baby is born. The risk of having a child with a chromosomal defect increases as a woman ages. The chance that your baby will have a trisomy disorder like Down syndrome is about one in 250 when you're 35 years old.
- You've had another test, such as a multiple marker screen or a nuchal fold scan that suggested your baby might have a problem. If this is the case, you may first have a detailed ultrasound scan to look for physical markers for Down syndrome and other defects. If the ultrasound indicates that there's still cause for concern, you may want to have an amniocentesis for a definitive diagnosis.
- You've already had (or been pregnant with) a child with a birth defect.
- You or your spouse has a family history that indicates your child may be at increased risk of inheriting a genetic disorder or you and your spouse is a known carrier of a genetic disorder, such as cystic fibrosis.

What are the risks of this procedure?

Once you've determined the procedure is correct for you, you'll want to weigh the small risk that the procedure may cause you to miscarry. You have a slight risk of uterine infection in the days following the procedure (less than one in 1,000), which can sometimes lead to miscarriage. These are all things you should discuss with your partner, your practitioner, and a genetic counselor.

What's the procedure like?

You'll most likely have a detailed ultrasound done first to measure the fetus and do an anatomic survey. This may happen on the same day as the amnio or a few days or weeks beforehand. For the amnio, you'll lie on an examining table and have your belly cleaned with an iodine solution. A doctor will use ultrasound to pinpoint a pocket of amniotic fluid a safe distance from both the baby and the placenta. Then, under continuous ultrasound guidance, your doctor will insert a long, thin, hollow needle through your abdominal wall and into the sac of fluid around your baby. The doctor will withdraw a small amount of amniotic fluid - about 20cc's - and then remove the needle. (The baby will make more fluid to replace what's taken out.) Withdrawing the fluid should take less than 30 seconds.

You may feel some cramping, pinching, or pressure during the procedure. The amount of discomfort or pain you may feel varies among women and even from one pregnancy to the next. If you're worried about a needle being that close to your baby, be assured that direct injury to the baby from amniocentesis is very rare. Your doctor will avoid placing the needle near the baby, but if your child happens to come in contact with it, he'll move away quickly just as you would if you bumped into something sharp.

When it's done your doctor check the baby's heartbeat for reassurance. You'll want to take it easy for the rest of the day and avoid any heavy lifting for the next two days. You may have some minor cramping for a day or so. About 1 to 2 percent of women will have significant cramping, vaginal spotting, or leaking amniotic fluid. Call your practitioner if you have any of these symptoms or a fever, since there's some chance that they could mean you're about to have a miscarriage. A small amount of fluid leakage is normal but should be reported anyway.

Note: If your blood is Rh-negative, you'll need a shot of Rh immunoglobulin after amniocentesis, unless your husband is also Rh negative, since it's possible that your baby's blood may have mixed with yours during the procedure.

When will I get the results?

Preliminary results are available in 3 business days. Final results are available in 7 - 10 business days.

All results will be forwarded to your referring doctor.