Health knowledge made personal
Join this community!
› Share page:
Go
Search posts:

Chorionic Villus Sampling: Is it Right for You?

Posted Aug 24 2008 1:49pm
MARTY MOSS-COANE: Welcome to our webcast. I'm Marty Moss-Coane. The birth of a baby is one of the most exciting events in a couple's life. Early in the pregnancy, one of their first stops should be at the obstetrician's office, who can monitor the mother's and the baby's progress. In some cases, the doctor might suggest a procedure known as chorionic villus sampling, or CVS. This is a test to determine if the baby has some kind of genetic problem. This is, of course, a very scary thought to an expectant couple, but it need not be.

On our webcast, we will walk you through CVS, so that you are fully informed about what to expect when you visit your doctor. Let me introduce our guests. Dr. Unjera Jackson is a maternal/fetal medicine specialist and Director of Obstetrics at Morristown Memorial Hospital in Morristown, New Jersey. Dr. Jackson, nice to have you with us. Dr. Joan Atkin is a medical geneticist, and Director of Genetics at Atlantic Health System, also in New Jersey. Dr. Atkin, welcome to you as well.

Let me begin with three words that I'm sure are unfamiliar to our audience: chorionic villus sample. Dr. Atkin, what do those words mean?

JOAN ATKIN, MD: The chorionic villus is an area that will eventually become the placenta. Sampling of that means that you take a piece of that tissue so that you can analyze it in the laboratory for a variety of different purposes.

MARTY MOSS-COANE: I'm interested, Dr. Jackson, when you suggest that a couple might consider chorionic villus sampling? What are some of the indicators?

UNJERA JACKSON, MD: Some of the indicators for chorionic villus sampling would be advanced maternal age. That is, a woman who is going to be 35 or older at the time of a delivery. If there is a specific family history for which chorionic villus sampling could be used to make a diagnosis of some sort of inherited condition or problem. A child who has been previously affected in that particular family with a chromosomal abnormality. I think those are sort of the basic categories of women who would initially be referred, or who might consider chorionic villus sampling.

MARTY MOSS-COANE: Did you want to add to that at all, in terms of those that would be considered for this procedure?

JOAN ATKIN, MD: Basically we're talking about couples that are at increased risk for a chromosomal problem. Dr. Jackson mentioned advanced maternal age and a previous child with a chromosomal problem. Also, if one of the couple is known to have what we call a balance rearrangement in their chromosomes that puts them at increased risk. And then, a couple that's at increased risk to have a baby with some type of genetic disorder, which they may know about from having a previous child, or from a family history, or also from screening testing that we do on certain groups of people.

MARTY MOSS-COANE: When in the pregnancy, which trimester is CVS normally done? Dr. Jackson?

UNJERA JACKSON, MD: Chorionic villus sampling is normally done in the first trimester. The specific time is between 10 and 12 weeks. Actually, sampling chorionic villi is a procedure which also can be carried out later in pregnancy. But for the purposes of diagnosis, early in pregnancy, to obtain information that will be useful for the management of the pregnancy, the usual time is first trimester, between 12 and 10 weeks' gestation.

MARTY MOSS-COANE: I'm curious. When you suggest this procedure to your patients, what kind of questions do they have? What do they want to know?

UNJERA JACKSON, MD: Usually they want to know exactly what the procedure involves, and what are the risks of the procedure. They also want to know what type of information specifically will be obtained by having the procedure done. The main concern, though, usually, is what risk they are taking for potentially losing the pregnancy, should they have the procedure done.

MARTY MOSS-COANE: What is the risk with CVS?

UNJERA JACKSON, MD: The risk can vary, depending upon where it's done, but in general the risk is in the 1-2% range. The procedure can be performed either transabdominally or transvaginally. Most of them are done transvaginally, going through the cervix, and that is where the majority of the statistics or data has been obtained, in terms of pregnancy loss.

MARTY MOSS-COANE: Who does this procedure? Is it the obstetrician? Is it the geneticist? Is there another specialist trained to do this?

UNJERA JACKSON, MD: It is usually an obstetrician who is specifically trained, usually, as a maternal/fetal medicine specialist, and even within that sub-specialty, there are people who particularly do it. Not everyone who is a maternal/fetal medicine specialist does chorionic villus sampling.

MARTY MOSS-COANE: I assume we're talking about a needle? Are we talking about a needle, Dr. Atkin?

JOAN ATKIN, MD: The transabdominal approach involves the needle. The transcervical approach does not involve a needle. It's a flexible tube, a latex catheter, and it's inserted through the cervix, similar to what the IUD placement is.

MARTY MOSS-COANE: Is it painful? I guess I'm back to you, Dr. Jackson.

UNJERA JACKSON, MD: There is certainly some discomfort. Any time an instrument is passed through the cervix there is some minor cramping. Additionally, the cervix may need to be stabilized by using some sort of tenaculum. Those things do cause some temporary cramping or pain. Also, the transabdominal procedure, certainly there would be some pain incurred at the time the needle is inserted into the abdomen. The pain is usually not significant, and it's usually very short in duration. Anesthesia is usually not used.

MARTY MOSS-COANE: I wanted to ask that, whether you think that's necessary or not.

UNJERA JACKSON, MD: I don't believe it is. There are some practitioners who, when doing transabdominal procedures, including CVS and amniocentesis, will use some local anesthesia on the skin in order to help minimize the discomfort, but in general, not. And for the transcervical approach, we do not inject any anesthesia into the cervix or anything of the like for those purposes.

MARTY MOSS-COANE: And, for the obvious reasons that we're talking about a pregnant woman and a developing fetus.

UNJERA JACKSON, MD: Exactly.

MARTY MOSS-COANE: Why would you go in abdominally versus vaginally? What does that give?

JOAN ATKIN, MD: It depends on the experience of the centers. There are many centers whose experience has initially been transabdominal, and that's where they have their most expertise, and other centers where they prefer a cervical approach. There are some times, depending on the placement of the chorionic villus, that it's more advantageous to go one route than the other. But I would say, in general, most centers specialize in one or the other.

MARTY MOSS-COANE: When you get the sampling, what is in that sampling, Dr. Atkin?

JOAN ATKIN, MD: That's tissue that are little villi. They look like little tree-like structures. And that tissue should be genetically identical to the fetus. Originally, the one cell that was formed when the sperm and egg met will multiply and multiply. Some of the cells will become the placenta, and some will become the fetus. So they should be genetically identical.

What we do with that tissue is very carefully tease out any maternal tissue that is near it, so we have very clean tissue that's from the chorionic villi, and then we actually culture that tissue in a laboratory, much as you think of culturing a throat culture for bacteria. We're actually keeping human cells alive in the laboratory. That's because in order to do chromosome studies or DNA studies, we need living, dividing tissue to analyze it.

MARTY MOSS-COANE: How long does it take to get the results, then?

JOAN ATKIN, MD: It depends on what we're doing. We also have two different kinds of results. We have what we call a direct result. Because we're dealing with something very early in pregnancy, the tissue is rapidly dividing, and we can often get chromosome results tentatively in about 24 hours. We also grow the tissue to get the final results, which takes about a week to 10 days, depending on the laboratory.

MARTY MOSS-COANE: Are these results reliable? I'm sure patients want to know that, whatever the results are. Can you take them to the bank, so to speak?

JOAN ATKIN, MD: It's a very good question, and by and large they are extremely reliable. We say that it's more than 99% reliable. I will say there is a difference between CVS and amniocentesis, and that is, sometimes you can get results that don't seem to make sense and don't accurately reflect the fetus. In those cases where we get ambiguous results, we might suggest a followup amniocentesis procedure later. That happens in about 1% of the cases.

MARTY MOSS-COANE: I'm curious what an ambiguous result looks like, and perhaps even with your geneticist hat you can explain that to us.

JOAN ATKIN, MD: Sure, that's a little bit difficult but, what we expect is to find out that all the cells show the same chromosome makeup. What we might find with a CVS result is that some will show one answer and some will show another. Sometimes the answer that they show doesn't make sense, because it doesn't go along with viability. Those are what we call ambiguous results. If on ultrasound everything looks fine, and yet the results don't look fine, that may be a time when we say Let's wait and get an amniocentesis to confirm the results.

MARTY MOSS-COANE: And an amniocentesis, obviously, is done a little bit farther along in the pregnancy, so you get more information, so to speak?

JOAN ATKIN, MD: It's not because it's further along, it's because it's a totally different procedure, and we're less likely to get results that don't reflect the fetus, because the cells we're actually culturing there have been shed from the fetus. The cells from the CVS are from the chorionic villi, and they will represent the placenta. As you can imagine, once the placenta and the fetus separates, changes can occur as those cells are dividing that don't reflect each other.

MARTY MOSS-COANE: We had talked a little bit earlier about the reason for having this procedure, if there are certain risks in this particular family or mother or couple. What kinds of results do you get? I'm just curious about the kinds of disorders, problems, abnormalities that might show up with CVS? I know we're learning a lot more about genetics, the role of genetics in development. Specifically, what are we talking about?

JOAN ATKIN, MD: The primary thing we're talking about is chromosomes. The chromosomes are the packages that hold all of the genes we inherit from Mom and Dad. Normally we expect to see 46 chromosomes in a human cell, 23 pairs. One of each of the pairs originates from Dad's sperm cell, and one from Mom's egg cell. Sometimes mistakes happen in making either the egg or sperm that result in an extra chromosome. Those tend to happen more with advancing maternal age. So those are the types of things we're looking for, to make sure there's the right number of chromosomes, and that there isn't any extra or missing chromosomal material. You could have just an extra piece or a missing piece that would have problems, or a rearrangement of chromosomal material.

UNJERA JACKSON, MD: Additionally, we can determine whether there's an abnormality of the sex chromosomes as well. Normally for a female there would be two X-chromosomes, and for a male one X and one Y, and there may be variation in the numbers of those. So that information would be obtained at the time of the CVS also.

One difference I do want to point out, and I think it's really important, that couples need to understand that when a CVS is done, we do not obtain the information regarding neural tube defects, which are abnormalities of the spine and the neural tube. We cannot get that information at the time of the CVS, but we are able to get that information at the time of an amniocentesis.

MARTY MOSS-COANE: I'm sure there have been times you've sat down with couples, and you have found some kind of problem due to CVS. What kinds of options do couples have? And how do you help them think through what those options might be?

UNJERA JACKSON, MD: Essentially there are two options with antenatal testing at any stage of pregnancy. One would be to continue the pregnancy, knowing what the potential outcome will be, but being prepared, and having additional testing and ultrasounds and maybe some other subspecialists involved, depending on what are the problems and organ systems involved.

The other option is to terminate the pregnancy. And that certainly is one of the reasons that couples do ask to have these various procedures done, because many times they would prefer to go that route than to have a child that's affected with a chromosomal abnormality.

MARTY MOSS-COANE: And that's clearly their choice?

UNJERA JACKSON, MD: That is clearly their choice.

MARTY MOSS-COANE: I'm wondering, too, when talking about CVS and talking about pregnancy, what percentage of pregnancies end up having problems associated with them, Dr. Atkin? Oftentimes, you can get a skewed view of what's a problem pregnancy or not.

JOAN ATKIN, MD: Three percent of all pregnancies, regardless of ethnic background, age, general health status, will end in a child with a major birth defect. Three percent. That includes all types of birth defects. Those related to chromosome problems, those related to single gene abnormalities, those related to developmental defects. Things related to an exposure a Mom had, and things we don't know why they happened.

On top of that, there are certain things that put them at higher risk. For instance, we talked about advanced maternal age and chromosome abnormalities. So a woman that's 35 at the time of delivery has a chance of having a fetus with Down syndrome of 1 in 270. A woman that's 40, it goes up to a little higher than 1 in 100. And then there is a variety of other things.

If a couple is at risk for having a genetic problem, and we're only talking about one pair of abnormal genes. For instance, cystic fibrosis. We can do prenatal testing for cystic fibrosis. If both of the couple are carriers, their risk is 25% to have an affected child. So depending on where they come from, what the problem is, and their age, there are different risks. But everyone has that 3% risk.

MARTY MOSS-COANE: I wonder, too, Dr. Jackson, thinking about the enormity of this information, whether you suggest that couples go and have some kind of counseling to think it through? Or is this something that you might do with your patients, for instance?

UNJERA JACKSON, MD: I like to incorporate the counseling. I certainly can provide a lot of information to my patients. I happen to be a maternal/fetal medicine specialist. One of the problems that we face is that many of the general ob/gyn practitioners either provide counseling or no counseling, and then proceed with trying to inform patients about having a CVS or an amniocentesis.

I really feel very strongly that there should be genetic counseling, because in addition, as Dr. Atkin mentioned, there may be things in the family history that the doctor is unaware of, or aren't sophisticated enough to really know specifically what lab the information might have to be obtained from, or what specific testing might need to be done, so that the maximum is done at a time of the invasive procedure.

MARTY MOSS-COANE: Sure, and these are such critical decisions that a couple has to make. Your thoughts about counseling, Dr. Atkin?

JOAN ATKIN, MD: It definitely needs to be done before the procedure. There are many things that can happen that aren't straightforward. For instance, the ambiguous results I mentioned. Those are not generally covered by a general doctor. There are many things that can come up other than Down syndrome, and it's important for the patients to understand that. And they can be fairly complicated, fairly complex and fairly sophisticated.

On top of that, it may be a couple that wants to decide: Do I want a CVS or an amniocentesis? And then, as Dr. Jackson mentioned, it's very critical, we may find something that the couple's at risk for that isn't even the reason they were sent to us. And many of those things require testing from the parental bloods before we consider a prenatal procedure. In fact, we'd like to see patients before they become pregnant.

MARTY MOSS-COANE: Absolutely. I thank you both very much for joining us and telling us about chorionic villus sampling. Thank you very much.

And thank you for joining us as well. We hope that you've learned something. I'm Marty Moss-Coane.

Post a comment
Write a comment: