Hi Dr. Smith,
This is not an embryology/andrology question at all, so I ask you not in your capacity as an expert, but just as a reasonable person. Well, actually, Dr. Jane might have the relevant expertise, so perhaps you could pass this question on to her?
I am pregnant with donor egg (from a donor who turns 32 this month) and donor sperm (from a donor who was in his early 20s at the time of the donation). My OB does not know the provenance of this pregnancy, so I have been offered amniocentesis, since my first trimester screening test (using my maternal age instead of the donor's together with nuchal fold measurement plus hCG concentration plus PAPPA concentration) gave me a 1 in 60 chance of carrying a fetus with trisomy 21.
Here are my questions. The odds of my carrying a fetus with trisomy 21 based on my age alone are 1 in 40. So in a way my first trimester screening test is reassuring, since it says I'm 1.5 times better off than my age alone would indicate. Given that what's actually relevant is the donor's age, and that the odds of my carrying a fetus with trisomy 21 based on the donor's age alone are 1 in 700, do you think it is reasonable for me to assume that my first trimester screening test gives me real odds of about 1 in 1000?
My second question concerns the odds of miscarriage if one has amniocentesis. The figure one typically hears is 1 in 200 to 250, but there's been a lot of press about a new study (Nov 2006 in Obstetrics and Gynecology with lead author Keith Eddleman of New York's Mount Sinai School of Medicine) that says that in fact there is no statistical difference in the miscarriage rate of those who have ultrasound guided amniocentesis and those who do not have amniocentesis. (The actual numbers were for the 3000 in the experimental group 1% miscarriage rate and for the control group whose size I don't remember 0.94% miscarriage rate. So, at most 1 in 1600 or so miscarriages are attributable to the amniocentesis.) Is this new study to be trusted? The idea is supposed to be that the old numbers were based on old techniques for amniocentesis, before ultrasound guidance was as good as it is now. (Did they ever just stick a needle in and hope for the best?!)
I ask all this because I really doubt that I'd be very able to deal with a child with Down Syndrome. I realize my chances of carrying such a child are very low, but since the cost of carrying such a child seem more than I can bear, I'm thinking amniocentesis makes sense (especially if the new study is to be trusted).
Thanks for your two cents'.
