The probability calculation and nuchal scan?

[Hedgehead]

I didn't know they did a calculation. I thought they just checked the nuchal fold then sent you on your way?

Apparently they do hormone blood tests, urine tests, a scan and take our data (like age etc) and give you a probability of the pregnancy failing or succeeding?

Is this true? I had no idea. I thought I was out of the woods! Had scan at 11 weeks, heartbeat, baby growing normally.

I have no idea but I'm desperate to know what happens cause my scan is on Monday ! I want to know if you get told the Nuchal measurement there and then ? I'm worries cause if it's high I will panic but it's still dependant on bloods and the same for if it's normal I suppose !

If you give consent for them to do this, they will do what is called 'combined screening' - this will take your age, the nuchal fold measurement and a couple of your blood results (b-HcG and Papp-A) and give you a risk for your baby having Down's Syndrome (or possibly other chromosomal abnormalities, like Edward's or Patau's).

This is no indicator for how likely it is for your pregnancy to fail or succeed at all - you can have a chromosomal abnormality and have a normal pregnancy! And vice versa, unfortunately...
But most likely, all will be well - if you had a heartbeat and a good nuchal result, chances are that everything will be just fine!

I hope this helps - I would have a chat with your midwife or GP, they will be able to explain this much better than I can

Good luck with your pregnancy!

Had my scan yesterday. I was told the NT measurement at the scan, then bloods were taken. I should get the overall results in a week or so. The nuchal measurement is just one of the variants, age and bloods being the others.

explains here

They will tell you the nuchal measurement at your scan - if not, ask them! If they take the bloods on the same day as your scan, you usually get the combined screening results within 2 weeks (depending on your hospital).

The results are given as a probability or risk of the baby having DS, e.g. 1 in 10 (10%), 1 in 100 (1%), 1 in 1000 (0.1%). This is because from the nuchal fold measurement and other factors (blood levels, age, etc) they cannot tell for sure one way or the other, they can only estimate the risk based on historical data from other women with similar characteristics. So high risk does not mean the baby definitely has DS, similarly low risk does not guarantee that it does not.

If the numbers are beyond a certain threshold (I think below 1 in 150) you will be offered an alternative test (CVS or amniocentesis) that gives a definite yes/no. But these tests have a small risk of miscarriage, so they are not done for everyone, and you do not have to have them if offered.

Hope that helps (I'm a medical statistician by profession )

I had my blood taken 30 minutes before the scan, and by the time the scan had finished (maybe another hour later as baby wouldn't get in the right position!) the sonographer already had the blood results back and could give me the full results...

I waited about 10 days for my results. I think you get them quicker if they come back high risk. Got told the nuchal fold measurement at the time of scan, bloods taken after (no urine test).

I can't believe I got this so wrong! I thought it was a probability of the pregnancy failing or not! So did DH. Maybe it was the way the ob was telling us. He mentioned nothing about Downs Syndrome or chromosomes at all!

How would the hormone levels indicate Downs? Why are they taken via bloods? What do they show? Surely if the pregnancy has made it to 12/13 weeks at the right size then the hormones levels are high enough?

Did you not get a pamphlet about it in the post? If you didn't I would advise going early and asking for some information/pamphlet about the probability. The pamphlet we got was very easy to understand and I assumed all hospitals would send out the same or similar ones to expecting mothers.

The standard nhs blood test measures two hormones, HCG and Papp-A. The levels of these are linked to the probability of the baby having DS, as are your age, NT measurement and gestational age of the baby. So all this information gets put into a computer program to predict the risk of the baby having DS.

DS babies are not much different in size to non-DS, so a scan measuring the right size at 12/13 weeks isn't really a predictor.

It is done by a blood test because it is far more accurate than a urine test.