Tuesday, January 28, 2014

Risk Assessments and Diagnostic Testing in Pregnancy

I want to spend some time talking about the risk assessment tests they can do now to gauge whether your developing baby is healthy or not. It’s absolutely amazing the technology they have now that can be used to give you a clear assessment of your chances of carrying a baby with either a neural tube defect or a chromosomal abnormality. To be honest, going into writing this blog I didn’t want to spend any time discussing all the things that can go wrong with your baby. In my work, I come across tons of articles on a weekly basis about the horrible things that can happen to a baby and it is all very sad.  So I wanted to stay upbeat and talk about normal development in this blog.  Also as awful and sad as these abnormalities are, they are rare. So at the end of the day they don’t affect many people in the general population. And it’s really not cool to get an already emotional pregnant woman stressed out about things she has a very slight chance encountering with her baby.  But now that I’ve been through some of this testing on my own I realized there is a lot on this topic that I would like to learn, as well I’d like to give my opinions on it. And hopefully this information is useful to other women out there.
One interesting thing about advanced risk assessment and diagnostic testing is when do we hit information overload? In my personal experience with this type of testing I fell just outside the normal risk range for a 33 year old women and we opted to have some additional testing done. As a person with a science background I understand my risk was essentially that of any 33 year old women and that is to say my risk was low so although waiting to have the next test down became a little stressful as the days went on, ultimately I understood our baby was most likely as healthy as could be. But what about people who don’t deal with science terminology and statistics on a regular basis? Do these risk assessments wrongfully stress them out? That’s just one train of thought that I traveled on while going through this process.

We’ve talked about the neural tube developing early along and representing the CNS. Defects involved with it have to do with the tube not closing up the tube properly. It can either lead to open defects or closed defects, closed defects are covered and less common while open ones occur in the brain and /or spinal cord are exposed. Neural Tube Defects (NTDs) occur in 1 in every 1000 births in the US.

Chromosomal abnormalities include missing or extra copies of a chromosome, or abnormalities within a given chromosome. A healthy fetus will have 46 chromosomes, 23 from mom and 23 from dad- each set of 23 has one sex chromosome (always an X from mom and either an X or a Y from dad). The other 22 chromosomes are autosomes and are represented two-fold in the set the fetus has. There are a number of extra copy diseases where the fetus has three of a given autosome instead of the normal two. Examples include Down syndrome which is technically known as Trisomy 21, Trisomy 18 (Edwards Syndrome), and Trisomy 13 (Patau Syndrome) where the number indicates which of the autosomes is in triplicate. Deletions are known as monosomy, one example is Turner Syndrome and occurs when a female has only one copy of the X sex chromosome. About 1.4 in every 1000 births in the US have Down syndrome, as a woman’s age increases her chances of giving birth to a baby with a chromosomal abnormality increase. For example a 30 year old woman has a 1 in 385 chance of having a baby with a chromosomal abnormality while a 40 year old woman has a 1 in 65 chance. (These are stats I got from reputable sources but they are not universal, you may see/hear slightly different ones).

Back in the day the only option to evaluate these conditions was an amniocentesis. This procedure is still done today as a last measure diagnostic of chromosomal abnormalities and neural tube defects. Nowadays before a women gets to that, there are a number of less invasive tests that can be done to assess the risk that the baby isn’t healthy. Now the key phrase is to ‘assess the risk’ that’s all these early blood tests and fetal ultrasounds can do, risk assessment- they are not a diagnosis. An amniocentesis is the only test that provides a diagnosis. Women nowadays have the option of taking a blood test in the first trimester along with a detailed ultrasound, or waiting until the second trimester to take a different blood test.  Physicians will make recommendations on which (if any) time point makes more sense for a given women, strongly dependent on her age but also her family history and personal history as well. If a women is over 30 these tests are explained early on by her doctors, and suggested to do at least one of them, but if a women is over the age of 35 the first round of testing is strongly suggested. (If you are under 30 and you don’t have a family history of any of this diseases, I would assume these tests are not recommended unless you felt strongly to have them done but I’m not under 30 so I can’t speak from personal experience on this).

The first test is most likely some variation depending on which genetic company your doctor’s office used. My OBGYN uses Integrated Genetics’ First Screen, a maternal blood test where they protein looked at is PAPP-A, commonly known as the Pregnancy Associated Plasma Protein A (it is more scientifically known as pappalysin 1). PAPP-A is an enzyme that cleaves a growth factor binding protein, it is thought to have a role in wound healing and bone remodeling.  This test only gauges risk of a chromosomal abnormality not of NTDs and it is done in conjugation with a detailed ultrasound of the fetus where the technician looks at the fluid filled space at the back of the neck. Extra fluid is an indicator for increased risk for chromosomal abnormalities. This measurement is known as nuchal translucency and it is used in combination with the PAPP-A blood test result to given an assessment of how likely it is the baby has trisomy 21 or 18. This combination of tests can be done between week 10 to 14.

The next option is a test done in the beginning of the second trimester, another maternal blood test this one looking at AFP- alpha fetoprotein. Again my doctor’s office uses Integrated Genetics and their Afp4 test, this test looks at risk for not just chromosomal abnormalities but also neural tube defects. This test compares this fetal protein to three maternal proteins, hCG (human chorionic gonadotropin, a hormone produced in early pregnancy that aids in setting up shop for embryo to grow. This hormone is known to most as the hormone detected in home pregnancy tests, it is also evaluated in the aforementioned First Screen test along with PAPP-A), along with two other proteins. The levels of all four are measured and a risk is calculated separately for chromosomal abnormalities and neural tube defects.
Now hopefully whichever test you decide on comes back putting you within the normal range of risk for a woman your age. It’s important to remember that this is only a risk assessment it’s not a definite yes or no that your baby is healthy or unhealthy. If your risk assessment comes back negative it means you fall within the normal risk range of having an unhealthy baby and that risk is small.  If your risk assessment comes back positive there are additional tests that can be done to either add to the risk assessment or go directly to the diagnosis phase. There is an additional risk assessment blood test for high risk women, that is women over the age of 35 or women under 35 that have tested positive on one of the maternal blood tests. This test looks at fetal chromosome fragments in maternal blood to give a clearer assessment of chromosomal abnormality in the fetus. The final option is amniocentesis, where amnion fluid is draw up through a long, thin needle with an ultrasound done before and after the insertion of the needle. This fluid can be evaluated for chromosomal abnormalities, neural tube defects, and certain genetic diseases. There is a slight risk of miscarriage and other complications from this procedure, such as bleeding and infection.

All-in-all this whole process can be scary and sometimes, as I mentioned above, give you case to freak out when really your baby is fine. Ultimately the silver lining to going through this nerve-wracking process is you come out knowing pretty definitely (depending on how far you go in the assessment) that your baby is healthy, which is more information than a women not opting to have these tests done would be armed with going into delivery.

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