Saturday, February 13, 2010

The Down's Syndrome Test

I had the first part of a 2 part Down's Syndrome test done last Monday.  Prior to this I had never thought much about Down's Syndrome or the testing for it.  This prompted me to do some curious research and I thought I would share what I learned because it interested me and some people have been asking questions about it since then.  I'm going to try and explain it all as simply as possible.  Let me first say that this test is not just for Down's Syndrome, although that is the most common diagnosis from it.  The test also determines the risk for Edward's Syndrome.  Both of these conditions are due to a trisomy at one of the chromosomes.  Humans have 46 total chromosomes in 23 pairs.  Everyone inherits 23 from each parent, including 1 sex chromosome from each parent.  In these syndromes, a baby will actually inherit an extra chromosome, so Down's Syndrome babies inherited 3 copies of chromosome 21 and Edward's Syndrome babies inherited 3 copies of chromosome 18.  Edward's Syndrome is much more severe than Down's Syndrome and only 5-10% of babies born with this condition will survive the first year.

Every pregnant woman has a standard risk for having a baby born with Down's Syndrome.  This risk is based purely on the age of the mother.  For example, my risk based on my age of 30 is 1 in 900.  The screening test they perform then adjusts that risk up or down based on the test results.  This test does not diagnose Down's Syndrome, it only assesses your risk.  If the test is "positive" it only means your risk is higher than normal and they will offer another test, such as an amniocentesis, to determine for sure if your baby has Down's or not.  The test I was given is a 2-step test.  The first part is completed between 10-14 weeks. I had mine done at 12 weeks.  The test includes the nuchal fold thickness measurement, which is a fluid filled space behind the neck of the fetus.  If this fluid filled space is unusually thick it is a preliminary indication that the baby may be at higher risk for Down's Syndrome or Edward's Syndrome.  From what I read, anything under 3mm is considered normal.  They measured my baby's at 1.6mm, well within the normal range.  After that test they took a blood sample from me to measure a couple of markers in my blood.  Each of these markers would show as either higher or lower than normal if my baby were at higher risk for Down's Syndrome.  If after these 2 tests I screened "positive" they would offer me the extra test.  If I screened "negative" I would have the blood test repeated in 4 weeks to be totally sure of the low risk.  I hope this makes sense to everyone.  It can be confusing.

Anyway, the results of my blood test came back on Friday.  Based on these results, they have lowered the risk of my baby having Down's Syndrome or Edward's Syndrome from the standard 1 in 900 to 1 in 10,000.  This is an excellent result.  Now, I just have to go back at 16 weeks and have the 2nd blood test.  Honestly, I don't think I really even need to do the 2nd blood test, but I won't skip it.  Its not a big deal, I am just kind of sick of having my blood drawn, especially since they have problems every single time.  Oh well, I will survive it. :)

On another note, I have had some people tell me that my baby is a girl based on the heart rate.  That is an old wives tale and it is not true at all.  My baby may very well be a girl, but not based purely on the higher heart rate.  This also piqued my interest, so I did a bit of Google searching and actually found a scientific study done to investigate this.  The study also determined the predictive value of 2 other common myths to determine sex, the Chinese calendar method, and the Draino method (which I had never heard of before).  It was an interesting study and proved there is absolutely no basis in fact for any of these methods.  They are no better than guessing at predicting sex.  I guess we will just have to wait for the ultrasound to tell us (which isn't fool proof either).  Anyway, here is the link to the study if anyone else is interested in it.

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