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.
The 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.