the results are inconclusive because of a mosaicism. Apparently, about 1% of the time, CVS results will return a mosaicism. This means that some of the cells in the culture have one chromosome arrangement and some of the cells have a different chromosome arrangement. In our case, specifically, 65% of the cells were normal and 35% of the cells presented with Trisomy 15 (three copies, not the normal two, of chromosome 15).
The good news is, according to the genetic counselor, about 90% of the time when there is a mosaicism the abnormal cells are from the placenta and not from the baby. The not as good news is they are more concerned than they would normally be because the cystic hygroma is present in addition to the mosaicism. However, to further confuse things, Trisomy 15 is not typically associated with the presence of a cystic hygroma.
I was a bit confused by all of this because I thought they were specifically testing a sample of the placenta, so to hear that they are distinguishing the cells from the placenta vs. the baby did not make sense. The genetic counselor explained that in fetal development, there is a specific point in time where the placental tissue and the embryonic tissue split, and each becomes an individual entity with its own cells dividing and each growing separately. Because they test the tissue from the placenta, and not from the baby, specifically, they have no way of knowing if the abnormal cells began appearing and began dividing before or after the placenta and the baby split from one another. So, in the 90% of the time where the abnormal cells are from the placenta, it is due to the cells not presenting and dividing until after the placenta and the baby are separate entities.
What does this mean?
Well...we won't know if we are carrying a baby with Trisomy 15 until we can do further testing. The genetic counselor is recommending that we do an amniocentesis, which will give us a more clear idea as to what is going on with the DNA. An amnio cannot be performed until we are 15 weeks, so we are a little early for that right now.
In the event that there is Trisomy 15, it is most likely mosaic Trisomy 15, which means it is not present in all of the cells. The extent to which that can be problematic depends on how many of the cells are affected and in which parts of the body they are located. If it was full-blown Trisomy 15, it is unlikely we would have made it to 14 weeks along because those pregnancies typically result in early miscarriage.
Regardless of whether or not Trisomy 15 (mosaic or otherwise) is determined to affect the baby, the cystic hygroma is still being treated as a separate issue, just possibly related. The genetic testing, which was supposed to help shed light on what caused the cystic hygroma, seems to have only made things more unclear...at least for the time being.
We are still scheduled for an ultrasound and to meet with the High Risk OB on Thursday. We were originally scheduled for some additional genetic testing, but that is on hold until we decide about the amnio and until we can actually have the amnio performed. (The other testing they were planning on doing was supposed to use the CVS samples, which we know will not provide results that we can rely on.) We are still hoping to hear on Thursday that the cystic hygroma has either diminished in size or gone away completely; anything but that it has grown in size or that there is evidence of fluid retention, edema or hydrops.
We will also be meeting with the genetic counselor again on Thursday to further discuss the test results we have gotten so far and other testing that should be considered moving forward.
In terms of expectations, we are still hopeful that things can turn out alright. Though, given our experience, we are also realistic about the possibilities. One of the toughest things to swallow, especially given all of the crazy testing we are doing, is that everything tested normal (DNA, autopsy, etc.) with our first pregnancy. So, while we continue to hope and pray that our test results come back normal, we know that there is no guarantee there either.
We will continue to post updates as we have additional information. Talk to you all soon!