I wanted to share our journey with Mosaic Trisomy 21 (T21) and Confined Placental Mosaicism (CPM) for Down syndrome. I did not find much online about this condition at the time so I thought some might benefit from this summary while waiting for results. Sending a lot of positive energy to those who are going through this.
1 Sept - 12-week scan (EDD updated to 12+3 days)
Completely normal scan, no anomalies found. Free beta hcg: 2.9895 MoM, PAPP-A: 0.2871 MoM (low). Adjusted risk for T21: 1:16
2 Sept - blood test done privately / NIPT (testing tool)
4 Sept - blood test result phone call - high chances of T21
At this point, our chances for a healthy baby were around 1-2% as the NIPT is able to detect T21 with high accuracy.
4 Sept - CVS (chronic vili sample) procedure through the NHS (diagnostic tool - sample from the placenta, tests both maternal cells and baby’s cells)
6 Sept - quick result: QF-PCR markers - evidence of T21 but inconclusive result. In this case, it is advised to wait for the long term culture result as they can’t tell whether the mother (e.g. placenta) or baby carry the T21 cells.
At this point, we were given information about termination for medical reasons given how uncertain a good result seemed to be.
18 Sept - long term culture / karyotype result: T21 likely confined to the placenta, referral to amnio
22 Sept - amnio (most reliable diagnostic tool, the gold standard - sample from the amniotic fluid, test baby’s cells only)
26 Sept - quick result: QF-PCR markers - all clear
At this point, our chances for a healthy baby improved to 50%.
6 Oct - amnio long term culture - all clear, confined placental mosaicism confirmed
In CPM cases, you will need to wait for the amnio long term culture to be absolutely certain that the baby has no cells impacted by Down syndrome. This is the longest possible route of diagnostics, unfortunately there are no shortcuts. Once CPM is confirmed, you will be given extra scan appointments to monitor fetal growth (there is a risk of smaller babies).
The care up until diagnosis was fantastic but when I was discharged from the fetal medicine unit we were left to our own devices with a high risk pregnancy that none of the midwives or GP has even heard of. It was a dreadful additional 6 months and if I could go back in time, I would go private after the diagnosis.
We were very fortunate to come out of this with a healthy baby but unfortunately chances are much higher for the types of mosaicism that also impact both baby and placenta. The condition is quite rare and studies only really picked up during the past 10 years ever since NIPT is a thing.
While there are really slim chances for a good outcome once the T21 cells have been detected by the NIPT test or the CVS diagnostics tool, it is a possibility. The specialist fetal medicine unit we attended in London had two of such cases over 5 years so it is definitely a rare occurrence.
Wishing everyone a lot of strength who have to go through this.