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Does BMI affect your Downs risk?

(18 Posts)
HeadFairy Sat 08-Aug-09 10:49:04

I've just been perusing my notes... I hadn't really bothered before, second baby and all.... anyway, I've noticed they've got my height really wrong... they've put me down at 152cms when I'm really 178cms tall, which has given me a BMI of 43. Obviously my BMI is not actually that high, however I seem to remember when I had my nuchal that the sonographer explained that they put together the nuchal results with the blood results and my age (plus I thought she said BMI as well) and they came out with the Downs risk. Surely if they got my BMI wrong then my Downs risk will be lower. Obviously that's brilliant, but I'm just wondering if that's the case.

Divvy Sat 08-Aug-09 12:06:22

Not sure if its just weight or bmi, but they put down my weight wrong with dc#4 and it gave a false high risk result. The fault wasnt pick up till I had been told the news either, not good at all!

They had just used an average weight, but I was very over weight!

When my correct weight weight was used, I was no longer high risk.

You need to maybe ring the tripple test departmant (what ever its called), they will look into it for you.

HeadFairy Sat 08-Aug-09 12:10:35

Thanks for that Divvy... so if I have a lower BMI I'm assuming my Downs risk will be lower than I was told? I'm due to have my anomoly scan in 2 weeks so I wonder if it's ok to leave it until then or whether I should call my midwife team?

ZippysMum Sat 08-Aug-09 12:16:07

I'm pretty sure that BMI doesn't come into the Downs risk calculation at all. more detail here
Not sure what happened with you, Divvy - but would be really interested to know!

Bubbaloo Sat 08-Aug-09 12:47:20

I really have no idea whether BMI plays a part,but I had a very high BMI(over 40) with both my pregnancies,and my Downs risk for both,was extremely low.

KatyS36 Sat 08-Aug-09 15:34:46

I had nuchal fold scan plus bloods (triple test?) a couple of weeks ago. The appointment was at a private clinic purely for Downs testing.

I was weighed as it was inputted into the stats equation.

I would definatly follow this up.

Divvy Sat 08-Aug-09 18:04:49

ZippysMum What happened was midwife or doctor didnt put my weight on the form, so when the tripple team got my results a standard weight was used. They used 10st, I was 16st 7lbs. I hadnt heard anything, so went to my doctors for the results, and was told I need to see a doctor. So waited then and there to see docto, who told me I had a high risk result, but felt I had slipted through the net as tripple test team should have rang me.

Left thinking I was having amnio the next day, only to be phoned by tripple test team, to be told I wasnt hight risk, and my weight had been entered wrong.

Later that day the doctor that owned the surgery that I had seen the day before, phoned me to say sorry, and it wasnt one of there shinning moments to upset a mum to be for no reason.

Its was a very bad 24 hours.

ZippysMum Sat 08-Aug-09 19:01:48

Thanks Divvy,
Wierd though - they didn't use my BMI for the test. Maybe there is more than one way of doing it?

motherinferior Sat 08-Aug-09 19:23:16

Why on earth would it? Down's is the result of a chromosomal abnormality; it becomes more likely with increasing age. AFAIK weight has absolutely no relationship to this.

ZippysMum Sat 08-Aug-09 19:34:11

Hi again,
Been reading on another thread - it seems that one of the components of the blood test can be affected by weight - so maybe that's where this is coming from.
Still interested about how they did mine, then hmm

Divvy Sat 08-Aug-09 20:09:54

Yes, blood and weight, age. are used for the formula.

Divvy Sat 08-Aug-09 20:12:48

I dont know why, but weight is very much part of it, not sure if its height as well ie then being bmi.

This is for the blood and nuchal scan combined tripple test.

TigerFeet Sat 08-Aug-09 20:16:43

Weight, rather than BMI, is definitely a factor in calculating Down's risk. I have no idea why, but I know that it is. If you have the triple test then your weight should be entered on the blood test form.

HeadFairy Sat 08-Aug-09 20:31:18

Thanks everyone, unfortunately they got my weight right , if it was based on BMI then my risk would have gone down!! As it was it was 1:400 at 38 years so I guess I shouldn't even worry about it. I don't like having a significantly higher BMI on my notes but that's just vanity!

Divvy Sun 09-Aug-09 13:20:53

Yes mine was left out. Since what happened with me (because of it - dont know) all blood forms that dont have weight on are now rejected.

I think 1:400 at 38 is very good smile

maygirl Sun 09-Aug-09 16:29:46

It doesn't affect your actual real life risk, but a correction factor for weight is used to get accurate blood test results, so they need your correct body size to get a valid risk factor for you. I think there's also a correction factor for race, so they need to get this right too!

Mouette Sun 09-Aug-09 17:51:25

Maygirl is right - weight does not affect the risk of Down's, but they have to adjust for weight when calculating the blood test results because what they measure is the concentration of a certain protein in the blood. 1/400 is lower than the average risk at 38, so the tests have in effect shown a reduced risk, but if you want to get a more exact calculation you would need to ask the clinic to redo their evaluation with the correct weight.

KittyTN Mon 10-Aug-09 12:16:16

I think it really pays to check all the details on your risk report. I think the weight that was used to calculate my risk was slightly off as they used my booking weight - 4 weeks of morning sickness later I was approx 1kg lighter. But I'm ignoring this!
I happened to notice an incorrect ethnic origin on my report. When I was Afro-Carribean my risk was 1 in 850, since 'becoming' a white caucasian my risk has reduced to 1 in 1700! The screening service quickly went through a double check of all the other details and recalculated over the phone.

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