More Math

I will be 40 when Boogie is born, so we need to do genetic testing. We decided on the quad screen and nuchal translucency instead of going directly to an amniocentesis, because of the chance of miscarriage. The quad screen is a blood test, and nuchal translucency a special ultrasound. In an amniocentesis, a needle is inserted into the placenta to get some of the amniotic fluid surrounding the fetus. There is a 1:340 chance of miscarriage if the amnio is performed at UCSF (the nationwide probability is 1:200, so all of us older mothers in the Bay Area are lucky). The difference is what the amnio is certain because you get cells from the baby, while the quad screen only gives you probabilities.

With my first trimester blood test, I screened negative for Down's and for Trisomy 18. Trisomy 18 is a different chromosomal disorder, where there are three copies of chromosome 18. Probability for Trisomy 18 was 1:11,000. So great. Probability for Down's was 1:220, somewhat better than the probability based on my age alone - 1:80.

We got lots of pictures of Boogie at the nuchal translucency ultrasound. And, the back of his neck measured 2.2 - 2.3 mm, which was in the desired range of 1-3 mm.

I have to wait until my second trimester blood test for an updated probability for Down's. Then we can make a final decision on the amnio. I do like certainty, so the amnio remains very appealing to me.