I thought I’d cover a topic today that doesn’t specifically have to do with pregnancy after infertility, but when I scan the boards I often see it as a source of angst, which is genetic screening. I find most of the explanations out there lacking, so let me give you mine.
Most women are offered screening for what’s called aneuploidy, or specific diseases caused by an abnormal number of chromosomes. The most common of these is Down’s Syndrome, or Trisomy 21. The tests also screen for trisomies 18 and 13, which are less common but usually life threatening. A screening test won’t tell you if the baby has a certain condition or not, it just calculates a statistical risk based on your age and a number of other factors. If you learn nothing else, this is what I want most women to understand, which hardly anyone tells you: what is called high risk or not is somewhat arbitrary. The first of these tests to come along was a blood test done in the second trimester called an AFP or alfa-fetal protein test. Other hormones have been added to this test, which has evolved into what’s called a quad screen. When the test first came out, there was a cut off number of what they would call high risk, and it was based on the risk of having an amniocentesis, which at the time was thought to be about a 1 in 200 chance of miscarriage. More recent tests have been given a number based on what the cut off should be to be able to diagnose the maximum number of babies without adding too many extra tests to normal pregnancies. I agree with something I heard a maternal fetal medicine doctor say once: that there probably shouldn’t be a cut off or a label of what’s normal or not, women should be given their risk and decide based on their own comfort level. For example, a risk of 1 in 150 would be considered abnormal on a quad screen, but less than 1% chance of having a baby with Down’s syndrome may be perfectly acceptable to some couples. A risk of 1 in 250 would be considered normal, but may seem high to a mother with 5 kid,s 2 of whom have special needs.
So after the AFP or quad screen came the early risk assessment, which is a combination of an ultrasound between 11.5 and 13.5 weeks gestation and a blood test. The ultrasound measures the baby’s nuchal translucency, or the thickness of the neck, and his nasal bone, both of which have a statistical relationship with chromosomal abnormalities. The advantage of this test is it is a little more accurate than the quad screen, and you get your results earlier. Then, in the past few years, we started offering patients something called the serial sequential screen, or integrated screen, which is a fancy word meaning a combination of the two older tests. The benefit if this test is it is the most accurate way of screening; however, not all insurances are covering this test, at least in my area.
So, if you have a screening test that shows a higher risk of Down’s syndrome, what are your options? The first option not many people talk about is to do nothing. If your screen result comes back with a risk of 1 in 50, you may be OK with a risk of 2%. If you would like a diagnosis, the gold standard is to do an invasive test. The most common is an amniocentesis, which is when fluid is removed from around the baby and tested for DNA. The results are as close to 100% accurate as you can get. Most women have heard that there is a risk of miscarriage from this exam. For years, we told women the risk was 1/200, now we are quoting 1/300 to 1/500, although there is speculation that it is even lower. The change is two-fold: first, ultrasounds have gotten much better, which makes it easier to insert the needle safely. The second reason is when the risk of amnio was first quoted, no one ever compared it to women without amnio who had miscarriages, and often it is women who are higher risk who are getting the test to begin with. The other invasive test is called a Chorionic Villi Sampling (CVS). It involves removing a small amount of tissue from the placenta. The advantage is it can be done earlier in pregnancy, between 10 and 12 weeks. However, there is a slightly higher risk of miscarriage compared to an amniocentesis, about 1 in 150.
There is a new test called cell free DNA. There are many companies offering this test, you would have to inquire with your provider as to which test they offer. The basics of the test is that there is a small amount of fetal DNA in the maternal blood, so DNA testing can be done by drawing the mother’s blood. The advantage is it is non-invasive, and carries no real risk, like the amniocentesis or CVS. However, although it is 99% accurate, it is not as close to 100% like the more invasive tests. Also, most insurances don’t cover it. The price can be anywhere from $200 to over $1000. My advice is that if you are interested in having this test, call the company directly and try to negotiate a lower price.
So, why might you want to have a screening test? The basic question you need to ask yourself is, is this information you would want to know before the baby comes? I think there is a perception that the only reason someone would want to be screened is if they would terminate the pregnancy. I have found that not to be the case. Many women feel better having the diagnosis prior to their baby’s birth, having had time to educate themselves and prepare. That being said, if you have an elevated risk on a screening test and choose not to have a more definitive test, would you feel better knowing there is a greater possibility and preparing yourself, or would that information just cause more stress? I actually viewed prenatal screening in the opposite way. I was 39 and 41 when I had my children and I already knew I was higher risk. I had the screening tests and thought, if it shows I’m low risk, I can be a little more reassured. If it shows I’m higher risk, I’m really no worse off than before. (I will talk specifically about older moms in another post – I think it’s a topic which deserves it’s own chapter.)
For some, especially those who have had a friend of family member with Down’s syndrome or similar disorder, a decision about how you would handle the diagnosis may have come long before you were pregnant. For some, however, the first time you may be considering this is when the test is offered. How to be screened and what to do with the information is a very personal decision. The only thing I might add, is that there may be assumptions from providers, family, or even yourself that your decision should somehow be different because you conceived after a struggle with infertility. Your journey up to this point will certainly color all future decisions, but it is one of many factors in how you determine the right course for you and your family from here on in.
I welcome any questions in the comment section, and have listed websites below for further information.
Originally published July, 2013