Sharon Praissman Fisher

Beyond the Egg Timer

Prenatal Screening and the AMA Mom

Are all of theses tests really necessary?

Posted Jan 11, 2015

   You will most likely be offered information about screening tests for birth defects at your first prenatal appointment.  Because some of the tests are done within the first trimester, they will be one of the earliest decisions you make about your baby’s care.   In this post, I offer you some background information and a decision making guide to help inform your choice.  As always, our aim is to help you make educated, informed decisions based on facts.  We have found great diversity amongst the way providers present these testing options.   Some present them as exactly that, options, while others present them as routine tests that everyone does. In the past they were considered standard care for moms over age 35, they are now offered to all women.  One 30 year old mom told us that her doctor told her she was “crazy” not to do them.  The practice I’m receiving care from simply presented the options. I will be 38 at delivery.  There is no “correct” or mandatory way to go, even for the mom over 35.

     Prenatal screening tests such as ultrasounds and specific blood work assess the probability that your baby may have a birth defect.  They do not diagnose a problem.  Diagnosis, or definitely declaring “this person has this condition”, comes from amniocentesis or Chorionic Villus Sampling (CVS).  The latter is offered if the former shows a higher chance than expected for a specific condition when compared to other babies with mothers of similar age.  

     It is important to understand that only a few birth defects are actually related to maternal age.  The two you have most likely heard the most about are Down Syndrome and Edward Syndrome (Trisomy 18).  Neural tube defects are not related to the age of the mother but more common in women who are obese, have inadequate folic acid intake, or are on certain medications.  Before you get to alarmed, only 2-5% of babies born to all mothers, regardless of age, have any type of birth defect. The majority of theses birth defects are not age related but may be genetic or stem from toxic environmental exposure (like smoking crack while you’re pregnant which you are probably not doing).  Even more reassuring, is that many of theses birth defects are not fatal and may not even interfere with your child’s long term development.  For example, a cleft palette would require surgery and may make feeding difficult and frustrating until it is corrected,but doesn’t prevent your baby from growing into a smart, strong, and healthy adult. 

      It is also important to put your baby’s actual risk into perspective.  Emma does that here  with Down Syndrome. Essentially, the chance you would conceive a baby with Down Syndrome at age 37 is equivalent to the chance that you would get audited this year.  The chance that a similarly aged woman would have a  child with  Edward syndrome is even less likely at 1 in 726.   It’s also helpful to understand the difference between prevalence and probability.  Prevalence refers to how many of theses cases exist for a specific population whereas probability means what are the chances of it happening to you.  All birth defects are more prevalent amongst younger women because they remain the majority reproducing.  Therefore, if you know someone who has had a baby with Down Syndrome,  she is most likely younger than you. 

      There are essentially three levels of pre-natal screening which your provider will explain to you.  They range from most comprehensive (done in the first trimester) to least comprehensive (done in the second trimester). The least comprehensive is also the least sensitive meaning it has the lowest potential of detecting any risk.  Overall sensitivity increases with maternal age but so do false positives. For example, if you are 40, then the screening will accurately detect Down Syndrome 96% of the time it has actually occurred, however, the chance of it showing  a false positive is 25%.   This means that of the actual number of pregnancies at age 40 in which the baby does indeed have Down Syndrome, the screening test will be spot on for 96% of theses, not that 96% of women will have a  baby with Down Syndrome.  In fact, only about 1% of 40 year old women will have a baby with this defect.  Of the 99% of 40 year old women who don’t have a baby with Down Syndrome, 25% will be told that it is highly likely their baby does have Down Syndrome even though this is not true.  In either case, the provider would recommend follow up with more invasive diagnostic testing like amniocentesis or CVS.  The good news is that the invasive tests are relatively low risk these days.  

       As a Nurse Practitioner, I was trained to only order tests if it alters the  treatment course.  I think this is sound advice and apply it here by asking three questions. Will knowing if your baby has a defect  alter whether you continue with the pregnancy, change where you will deliver the baby, or help you better cope with anxiety? If you answered yes to any of theses questions, then you are probably best off with the most comprehensive of testing that can give you the earliest results.   This will empower you to make decisions and plans should a problem be confirmed by the diagnostic invasive testing.  This may mean transferring care from a home-birth midwife to a tertiary care hospital or lining up specialists who can best treat your baby.  You can lower anxiety by learning about the condition or connecting with an advocacy group or parents of other children with the same condition.  If you think termination may be an option, then it is safer earlier in the pregnancy.  It is important to discuss theses scenarios with your partner prior to getting pregnant.  The time for major surprises in personal philosophies  isn’t when you are 12 weeks pregnant with a baby with a major birth defect (it’s more of a 3rd date kind of thing).   Understand, your feelings may completely change with the pregnancy as well.  You may simply not know how you will respond until you are in the situation and that is ok. 

     If you answered no to all of theses questions then seriously consider why you are having the testing done.  You may be best off with the least comprehensive of options or no testing at all.  In some cases, too much testing can lead to more anxiety.  This is especially true as the chance of false positives increases with age.     If you are on the fence, have an honest discussion with your partner or a trusted friend who is educated about the topic.  The most important thing is to choose based on what feels right to you.

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