Diagnostic tests

[Sid]

I'm 8 weeks pregnant with my third child and am wondering for the first time whether to have any additional tests, other than the 20 week scan, eg. nuchal fold, or blood test for Down's Syndrome. For my first two, I didn't want them as I had no idea what I would do, should I have a high probability of bearing a Down's child. I felt very much on principle that I ought to give birth to the child my husband and I conceived, come what may, as it was our choice and privilege to be able to have children. This time I somehow feel more worried, perhaps because I'm older (35) and also wondering how I will cope with a third (even though I do really want it), let alone potentially a special needs child. What have others done? Have diagnostic tests reassured you? Have you ever had a termination as a result of a test? Have you had a test and ignored the result? I'd love to know.

I suppose the way to look at it is that both the nuchal scan and the blood test are predicitve of risk factors rather than being diagnostic. Rather than them telling you whether you are going to have a baby with Downs or not its better to view them as the means of deciding whether to have trully diagnostic tests such as amnio. The advantage of the nuchal and blood tests is that they are non-invasive whereas other tests give real answers but at the same time carry a risk of miscarriage. The risk factor you are given helps you weigh up the risk of miscarriage if you want to be sure but don't really tell you anything more than that.

Oooh, this is forcing me to kick start my brain! I'd not given it much thought before now. This may be utter gibberish but could this be how it works:

Any 36 yo woman would have a 1/150 chance of giving birth to a Downs baby. By looking at the nuchal fold for her baby, the risk of that baby (with a specific nuchal fold measurement, born to a 36 yo woman) being Downs could have been 1/2169. Reducing this risk factor by 20% to allow for the inaccuracy of the nuchal fold measurement gives an adjusted risk of 1/1735. (2169 x 0.80 = 1735)

The risk factor of the nuchal fold measurement is the risk of that particular baby being Downs. The age related risk is the risk of that mother having a Downs baby. They're not the same thing. "You" personally have a 1/150 chance of having a Downs baby. The baby being scanned has a 1/1735 chance of being Downs.

For example, the age related risk for a woman carrying twins would be the same for each twin. The nuchal fold based risk could be wildy different for each twin.

See, clear as mud!!

Bells2 - The Wolfson Institute at the Royal London does private tests - they have a website but can't find it's address at the moment.. They do a nuchal scan and blood test at 12 weeks (and they don't like you to book before 9/10 weeks) followed by a second blood test at 15/16 weeks. The cost is £145 which includes an amniocentesis if you have a high risk and choose to have an amnio.
Also, the fetal medicine centre (Devonshire Terrace? I think? Off Harley Street), does a nuchal scan plus the early blood test. This was £110 two years ago. Think the address is www.fetalmedicine.com, but definately on Google.