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Anyone know why you're not meant to use scales which do BMI/body fat analysis when pregnant?

(13 Posts)
herplaceby Sat 08-Jan-11 22:07:04

I suppose you're get a damn funny analysis, wouldn't you? But are they bad for the health?

They're the kind of scales you find in gyms, for the uninitiated. Maybe you'd get two BMIs, your own and your baby's. grin

suzym1984 Sat 08-Jan-11 22:22:25


I recently bought some scales which have a BMI/ body fat/ water analysis built in. In the instructions it says that they are not harmful but will give a strange reading so not to use them. This makes sense to me, as at 36 weeks pregnant I know my baby is laying down loads of fat, so that would mess up the reading.

StiffyByng Sat 08-Jan-11 22:43:06

I'm using one for the first time ever (and last I hope) as I'm in a research project at the hospital. Not sure how it works because the first time I was weighed, and winced at the appalling results, they immediately said not to worry, and that it's all meaningless in pregnancy!

lunafire Sat 08-Jan-11 22:56:00

Not sure of any harmful issues but surely any BMI measurement taken during pregnancy is completely meaningless as it would include the weight of the baby, amniotic fluid and the placenta and impossible to separate from your own body weight.

YellowCecil Sun 09-Jan-11 07:18:39

I think it is because BMI is calculated differently when pregnant. It is worked out by plotting height vs weight on a graph. Different graphs are used for men and women (as they have different body shapes!), and a totally different set of graphs are used for pregnant women, depending on how far along you are.

The scales that "automatically" calculate your BMI have the normal graphs programmed into them but they just don't have options for the pregnancy, and therefore would give you a very skewed result.

If you want to know your BMI you'd need to ask you midwife if she could work it out for you. But chances are she'll tell you not to worry about it too much - unless you are gaining excessive weight pregnancy is a time to stay healthy but not to get too frantic about a changing body shape.

violetwellies Sun 09-Jan-11 10:40:11

Ive always thought the whole BMI thing was bullocks as you can see if youre carrying a bit of extra pork but if you are fit - my competing weight is 9stone 5 then 'extra' muscle will give a higher BMI, - so a fitter person can look less healthy by using these scales hmm.

Deliaskis Sun 09-Jan-11 18:46:36

Hmmm...I think the body fat ones work differently to the straight BMI ones. I was told at a gym that the body fat ones work by sending an electrical current through your body, and the speed at which it travels tells it how much fat there is, as the current travels through fat at a different speed than through other tissue.

It always says it is perfectly safe (when not pregnant) to have this current travelling through you, and I suspect the pregnancy thing might be that they haven't enough data to confirm that it's definitely OK for the baby?


onimolap Sun 09-Jan-11 18:51:17

AFAIK, it's simply because they cannot give an accurate reading as they are not calibrated for the ever growing bump

cowboylover Sun 09-Jan-11 19:22:08

Deliaskis: Thats what I was told when I asked in the gym as well. Its the electrical current thing thats not tested.

herplaceby Sun 09-Jan-11 22:24:41

Thanks so much everyone. Most reassuring! grin at wonky measurements due to fattening baby...

bunny1975 Sat 30-Jun-12 20:23:06

I am 32 weeks and just read the instructions saying not to use body fat scales when pregnant - I was really worried but only used them twice about a month ago. Hoping all is ok. Trying not to worry :-(

zoobaby Sat 07-Jul-12 00:09:17

My home scales do the BMI thing and the booklet says it measures using a current. I still use for regular weighing and the way I figure it - what harm can a watch/clock battery do?

snakesmissus Mon 27-Jun-16 12:58:40

so kinda looks like it may or may not be dangerous for bubbs!? :-( oh well, baby tissue being bones etc etc i was asssuming would be measured as our own mass. i was more interested in my body fat analysis as i thought a wee bundle of bones and tissue wouldn't count as fat....

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