This week we had another ultrasound. This time it was for genetic testing. We were screening for Trisomy 18, Trisomy 13 and Down Syndrome.
Trisomy 18 is called Edwards Syndrome and happens when there are 3 as opposed to 2 copies of chromosome 18. The syndrome has a very low rate of survival, resulting from heart abnormalities, kidney malformations, and other internal organ disorders.
Trisomy 13, also called Patau Syndrome. It is an extra or third copy of chromosome 13. An extra chromosome here will interrupt the normal course of development, causing heart and kidney defects.
Before we took the tests, which include a blood draw and ultrasound, we had a statistical risk of 1 in 190 for both Trisomy 18 and 13. After the test we were reduced to 1 in 3,781. Both babies were considered within a safe range, no further screening is required or recommended.
Down Syndrome is an extra chromosome on chromosome 21. This impairs cognitive ability and physical growth. For this test they use the Nuchal Translucency Scan, measuring the fluid behind the babies necks. We were told that under 3mm is good.
Both ultrasound technicians were very positive about our twins Nuchal Translucency, which was under 2mm on our ultrasound this week and last week. Twin A was measuring 1.7 mm. Twin B was 1.8 mm.
I walked into the doctor’s visit after the screening very confident. So you can imagine our surprise (Adam was with me, and Jack & Ben) to find that Twin B was showing ‘increased risk’ for Down’s. I little millimeters difference between Twin A and Twin B put one in a safe range and one in an increased risk range!
Before we had the tests, both twins had a 1 in 106 chance of having Down’s Syndrome. After the test Twin A had a 1 in 309 chance and Twin B had a 1 in 252 chance. So taking the test dropped our odds of both kids having Down’s Syndrome, just not enough for the doctor to feel comfortable.
If we want to do more testing there are a few options.
We could have a Chorionic Villus Sample (CVS) done. It is similar to an Amniocentesis, but instead of drawing fluid from the amnio sac, they take a sample of the placenta. At this point, the chance of miscarriage from the CVS test are about the same as having a baby with Down’s Syndrome.
Or we can wait another month and have the United Screening Approach. It is simply a blood draw that combines your first and second trimester screenings. It detects at least 97% of cases of Down syndrome with an overall false positive rate of 5%.
We had planned to do the United Screening Approach even before the tests came back, as we have with all our other pregnancies. We decided to wait on the results of these tests before we decide anything further. The blood draw for this test can be performed anywhere from 15 – 22 weeks into the pregnancy. I’ll let you know how it turns out…Pin It