The genetic counselor then went on to tell me she was sorry and that the results are 99% accurate and that I need to find a pediatrician that will take a child with Down Syndrome and get ready for having a baby with down syndrome. So they offered the MaterniT21 screening and it came back “positive” for down syndrome. The nuchal fold was normal and the nasal bone was present but my PAPP-A is low and my HCG is high. They broke those results down to a 7% chance that my baby will be born with down syndrome and a 93% chance that my baby will not have down syndrome. My NT scan came back with a 1:13 chance for Down syndrome. I am 26 years old and pregnant with my first child. UPDATE: For those who may take in information by listening more so than by reading, the subjects covered in this post are the topic of Episode 1 of this blog’s podcast, which can be listened to here. The professionally recommended resources for Down syndrome can be found at the Prenatal Resources Tab on this site. Lastly, professional guidelines recommend that patients receive written informational resources about the tested-for condition when receiving a screen-positive result. Since this tool became available, it is the one I most often use in answering expectant mother’s question of “what does my cfDNA screen result mean?” You can, too, simply by accessing the Perinatal Quality Foundation’s helpful PPV/NPV calculator at this link. The NPV can tell you the probability that you are not having a child with Down syndrome. The same calculator also provides the negative predictive value (NPV) for your screen results. Then, you can enter the lab’s sensitivity and specificity information and press “Calculate” to receive your PPV. The other method is to enter your prevalence, if you had a previous conventional screen, such as nuchal translucency combined or the Quad test. Then, by pressing “Calculate” you will receive your PPV based on a screen-positive cfDNA screen. After entering this information, then you can enter the sensitivity and specificity of the cfDNA laboratory (or simply use the default settings for a close approximation). ![]() The default setting is if you are an expectant mom who had cfDNA screening as an initial screen, then you enter your age and the condition the screen reported detecting. The Perinatal Quality Foundation created a PPV calculator. Then, I’d link the commenter to this post for the simple chart in the middle that shows the PPV associated with the age of the expectant mother, with the PPV rising with the age, just as the chance for having a child with Down syndrome increases with the age of the mother.īut those figures were based on my own calculations, and, being a lawyer by training, the joke is that lawyers go to law school because there’s no math.įortunately, there is now an online tool that provides more precise calculations to determine a cfDNA screen results PPV. This was a concerned raised in 2013 with the way cfDNA screen results were being reported and leading to much confusion on what a screen-positive meant for the actual probability that the pregnancy was positive for Down syndrome. That fact sheet explains why the critical number is not the claimed “99%” but what the screen result’s positive predictive value (PPV) is. Is this correct? Please help.Īfter explaining that cell-free DNA screens like Sequenom’s MaterniT21 or Illumina’s verifi are never positive, and linking to this post on why saying those results are “99% accurate” amounts to malpractice, I then would link to the National Society for Genetic Counselors (NSGC) fact sheet on cfDNA screening. I asked what that meant, and she said I had a 99% chance of having a baby with Down syndrome. Today, my OB called saying the results were positive. Usually, the comment continues along these lines: This is a question that gets asked at least once a week in a comment to one of the hundreds of posts on this blog: my blood test just came back for Down syndrome–what does it mean? Fortunately, there’s an on-line tool to help understand these results.
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