Amniocentesis FAQ's

If your doctor has suggested amniocentesis -- a procedure in which some of the amniotic fluid around the fetus is removed for genetic testing -- you probably have a lot of questions and concerns:

  • Is the procedure safe for you and your child?
  • What are the chances that an abnormality will be found?
  • What decisions will you be faced with if there is an abnormality?

Read on for answers to these and more.

When a couple finds out that they're going to have a baby, it's a cause for celebration. But for some couples, there are questions about the health of their newborn. With all the advances in medicine, doctors and their patients can learn a lot about the development of a fetus, and one of the tools that's commonly used is amniocentesis. This is a procedure which involves removing a small portion of the amniotic fluid which surrounds the fetus. It was first tried many years ago, and today is used in the second trimester to determine if certain birth defects are present.

Question: What is in the amniotic fluid that makes it so important for amniocentesis?

Answer: Those are fetal cells, cells that have actually shed from the fetus. They come from the skin, from the GI tract, from the lungs, and from the bladder. We're actually looking at fetal cells when we do testing from the amniotic fluid. So it's not the fluid per se that's important, but the cells in the fluid.

Question: What indicators would be a reason to suggest an amniocentesis?

Answer: The primary indicators for amniocentesis would be the mother being age 35 or older at the time of the delivery, a known family history for which genetic antenatal testing can be used to determine whether the baby is affected. A prior child who has been affected with a chromosomal abnormality or some other inherited condition. And, additionally, an abnormal ultrasound in and of itself could be an indicator for an amniocentesis.

And also, during the second trimester, we routinely offer triple screen tests, which includes looking at maternal serum alpha-fetoprotein, something called the free-beta, and an estriol level, to come up with a calculated risk which uses the patient's age, the number of fetuses she's carrying, and a variety of other parameters to calculate a risk. And if she's at increased risk, based on this particular blood test, then that would be an indication for proceeding with an amniocentesis also.

Question: Are multiple births an indicator for amniocentesis?

Answer: Multiple births in and of itself would not be. The criteria would be age, prior history, an abnormal fetus being picked up at the time of an ultrasound, or an abnormal triple screen.

Question: Could you explain what an abnormal triple screen means?

Answer: This is the blood test that is offered between 15 and 19 weeks, although performing the test earlier is better, because then you have time to do the additional workup. Again, looking at the three parameters that I mentioned, in order to come up with some numbers that determine whether the patient's at increased risk, for example, for Down syndrome, which is trisomy-21, or trisomy-18, or open neural tube defects.

The triple-screen test is one of those tests that is fairly much routinely done by most obstetrical practices. A lot of patients are worried about what they've been told. It's false negative or a false positive.

The terms false negative and false positive are misleading because the test actually recalculates your risk of having a baby with Down syndrome. It does not say "yes" or "no". Up until recently, all we had to deal with was maternal age. If we just use maternal age alone, 35 or older, we were picking up on 6% of Down syndrome. So we wanted to do something that would help us with the women 35 and younger. Over time we've come up with this particular test that will recalculate the risk.

What we use as the cutoff is the same risk as you would see with someone who was 35 or older. So if it turns out that your risk of having a baby with Down syndrome, based on the triple-screen, is 1 in 270, that's a 35-year-old's risk, then you're offered amnio. Now, think about that. If your risk is 1 in 270, that means 269 out of 270, it won't be Down syndrome.

So we don't like to scare the patients. We just want them to know that they're at this risk, and they're offered an amnio. They don't have to have it if they don't want it.

Question: Who is qualified to do amniocentesis? Is this done in a doctor's office, is it inpatient, outpatient?

Answer: The amniocentesis is usually done in an outpatient setting in the doctor's office or in a perinatal and antenatal diagnostic testing center. The test most often is performed by an obstetrician, maybe a generalist, or a maternal fetal medicine specialist. Occasionally a radiologist may actually perform the procedure.

It is done under ultrasound guidance. What that means is that, as a part of the entire procedure, a full targeted ultrasound should be performed. However, depending upon where the test is being done, the full targeted ultrasound may not be performed. It may be a more basic ultrasound.

amniocentesisThe test itself involves localization of a pocket of fluid. The patient's abdomen is prepped to maintain sterility, and then a long, thin-bore needle is passed into the abdomen under ultrasound guidance, with or without local anesthesia. Some doctors use local, most of us in fact do not, and while visualizing the needle with the ultrasound, going into the fluid, we actually then aspirate or remove approximately 30 cc of amniotic fluid. That is two tablespoons. That is an insignificant amount, because at that stage of pregnancy, there is about 150-300 cc of fluid. So the baby really does not miss this, and it is regenerated, and there is not a problem just from removing that very small amount of fluid.

Question: What are the risk factors associated with amniocentesis? A lot of patients see the size of this needle and their anxiety goes up!

Answer: Their anxiety does go up, although we tend to reassure them by saying "Although the needle is long, it's thin-bore." It's a 20-22 gauge, which may not mean anything to them, but it's a very, very thin needle, and that's what's important in terms of needle size. Not the length, but what the diameter of it is.

The risk, actually, the overall quoted risk in this country for losing the pregnancy just from having the procedure done, is approximately a half of a percent. That is 1 in 200 procedures. Depending upon where it's done, the risk might actually be a little bit less than that, and we quote, I do to my patients, about 1 in 300 to 1 in 400. But overall, it's about a half of a percent, or 1 in 200.

Question: Are there certain women who more at risk to lose their pregnancies?

Answer: That's one of the things that has to be factored in. What is the background loss rate in a given population that has to be taken into consideration? Some of these patients would obviously have lost their pregnancies whether they had the procedure done or not.

Some of the things that may complicate or may increase the complication rate include previous bleeding or if there's a bloody tap at the time of the procedure. If the needle has to be inserted more than one time in order to collect sufficient amount of fluid. And certainly, some concern in a multiple gestation.

We tend to do the procedures in twin pregnancies quite a bit. For higher order multiples such as triplets and quadruplets, there tends to be less invasive diagnostic testing, if you will.

Question: What happens with this amniotic fluid? What do you look for, and how do you find the information?

Answer: The fluid is put into tubes, usually about three different tubes. When it comes out, it's a clear to yellow color. If you look at it, you can't see those cells I told you about. What we do, though, is take the tubes to a laboratory, put them in what's called a centrifuge, which is a very fast spinner. And the cells, being heavier, will go to the bottom. We'll see a little white button on the bottom. We take out those cells and put them in tiny little culture dishes, and actually culture the cells, and make them grow and divide. Because it's only dividing cells where we can actually see chromosomes when we do fancy manipulations in the laboratory, put them on slides, stain them, and look under the microscope.

We also get a level of the alpha-fetoprotein, which is a protein produced by the fetal liver, and will be elevated if there's an opening in the fetus. Most commonly, we talk about neural tube defect, which is an opening along the spine, but you could have an opening in the front, too, where there's stomach or intestines out -- any type of opening will increase the level of AFP, we call it.

The fluid itself, not the cells, we can measure the alpha-fetoprotein level right away and get an answer regarding that. But the chromosomes and any type of genetic testing that involves DNA, we need to grow the cells in the laboratory.

Question: How long does it take to get definitive results with amniocentesis?

Answer: It takes about, depending again on the laboratory, about a week to 10 days to get the results of the chromosomes. If we have to do some specialized testing, it'll take us that long to grow the cells and then we have to send them off into a very specialized laboratory. Sometimes only one laboratory in the country or one laboratory in the world does the testing.

So if we have to do DNA testing, it takes a little bit longer, maybe a few days longer, maybe even a couple of weeks longer. But the most common type of testing, the chromosomes, we should have results within 10 days.

Question: Can you rule out most birth problems or birth defects with amniocentesis if you get clean results? Is that kind of smooth sailing for the rest of the pregnancy?

Answer: That is a great question, because most patients think normal amniocentesis, normal baby. We talk about background risk of 3% of all types of birth defects. Only one small portion of that are chromosomal problems. So we're not ruling out everything by doing that testing. We're ruling out things like Down syndrome and other chromosomal problems, and we're only looking at specific genetic disorders if we know the couple's at risk for them. It's not done routinely.

Other types of birth defects will, however, be picked up by the targeted ultrasound. But all birth defects will not be picked up by the amniocentesis.

Question: What kind of counseling or conversations do you have with your patients? Since you're talking about the second trimester, they're well along in their pregnancy and they have to make a hard decision about what to do with this baby. It's got to be tough in the second trimester.

Answer: It is a much more difficult situation. Many times the mothers are aware of fetal movement. They're beginning to show. Others know that they're pregnant. And the diagnosis in a sense is relatively late, although it's still in the first half of the pregnancy or the second trimester. It does make making a decision that much more difficult, but again, the options are the same. Either continue with the pregnancy, with the appropriate workup and other sub-specialists who need to be involved becoming involved, and any other diagnostic testing that needs to be done being done. Or a decision is made to terminate the pregnancy.

Here, there are several techniques or methods that may be used to accomplish that. And we usually have some conversation about what the various methods are.

Question: Do you help prepare for a delivery, for perhaps a problem delivery, or are there things to sort of help it along? Answer: Certainly we do. We talk to the parents about what to expect when the baby is born. We have them meet with the neonatologist. They're specialists who deal with newborn babies that have problems, or premature babies. If the baby's going to have a heart defect, they meet with a cardiologist and a cardiac surgeon. If there's an open spine defect, they might meet with a neurosurgeon, or doctors that specialize in taking care of those types of children.

Depending on the problem that we see, we have the parents meet with the specialists they need to meet with, and actually we have them go into the neonatal intensive care unit to see what it's like to have a baby there.

This is a chance to look around, and talk to other parents, so that they will be ready to have a child with special needs. And we let them know what that's like to have a child. We might introduce them to other parents that have a similarly affected child. They might even go to some of the special schools that their child might need.

The other thing, we usually have some discussion regarding the mode of delivery. For the most part, we can anticipate vaginal delivery, but for some of the physical anomalies in particular, we might say a Cesarean delivery would be better for the baby. So we have those discussions with the couple as well, in terms of when we anticipate the delivery, as well as how we anticipate delivering the baby.