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*Answered* Why do Clearblue OPK's ask for FMU?

(8 Posts)
BabyBumpHopeful Sun 01-Feb-15 04:46:47

I've been reading this question a lot lately:

"Why do IC's tell you not to use FMU but CB's want you to use FMU?"

The reason for this is essentially for the same reason (high concentration of urine = high LH) but it's because the tests work in different ways. To understand why there's this different, you need to understand how the tests work.

The IC's work by the LH in your urine reacting with a chemical imbedded into the test line strip. This reaction turns the test line into a colour and the higher the concentration of LH the darker the result (it will almost always show up a little but only when the test line is as dark as the control line is it a positive result). Using FMU (or highly concentrated urine) for a test like this would risk false positives.

The CB tests work by monitoring your levels of LH and determining what your "normal" range is (which is why you re-use the monitors). Using this normal, they are able to detect when you are having a surge, or rapid increase in LH, which indicates ovulation. So, because FMU has the highest possible concentration, when that highest changes and becomes even HIGHER (as it does when you're ovulating), the monitor realises you must be ovulating, or about to, and gives a positive result.

I was using IC's but I've since decided to switch to a CB digital monitor (the one with the smilies). The reason for this is because it's easier for me to test on first waking (as opposed to remembering to test at the same time every day later in the day with an IC) and also because I found it difficult to be 100% sure if I was getting a positive or not because I often had quite dark lines.

Hope this helps!

MaMaPo Sun 01-Feb-15 04:56:08

Very helpful! I'm using the fertility monitor which also asks for fmu. I also assumed that it had something to do with calculating the relative presence of estrogen? Any ideas if that's plausible?

BabyBumpHopeful Sun 01-Feb-15 05:13:25

You are right the big one (the one I don't have :P) is the most advanced kind and measures both oestrogen and LH. They're months and months of uses and very personalised (great machines but too $$ right now... ask me in a couple more months of TTC!!)

Here's a link from their site:

MaMaPo Sun 01-Feb-15 05:27:54

Baby bump, I bought mine second hand off eBay and it works fine. I'll definitely sell mine on when I'm done with it - but hopefully you get your bfp before then!

PurdeyBirdie Sun 01-Feb-15 10:09:32

I have a CBFM and have never, ever used it! Still in the box!

MissMrsMummy Sun 01-Feb-15 14:25:33

Thanks for posting babybump

Would you recommend the cbfm? Maybe I should get one? Ics have been ok for me so far and my temps confirm ov so I hadn't considered buying a cbfm.

BabyBumpHopeful Sun 01-Feb-15 16:03:24

This is the one I have: the, Clearblue Digital Ovulation Test.

I would think the CBFM would be very good, but no machine or test means you will 100% get pregnant, they should be more about ensuring you DO ovulate and learning more about your body and hormones. Because you already know that your OPK's and temps confirm OV you shouldn't need one but that doesn't mean you might not want one.

The CBFM is more expensive that the digi OPK so I'll give the cheaper one a go first and hope I get success. If I don't, I might need more advanced stuff to find out WTH is going on smile

I'm only cycle 2 (but have been studying/learning since April 2014) and this first month was just DTD EOD. I found that as I couldn't be 100% sure I ovulated or when (CM isn't that reliable) and I didn't like that constant wondering. I think knowing for sure I've ov'd (well at least having tests that show I did) and when should help alleviate some anxiety.

It is a luck game mostly. You can do everything right (eat/drink right, sex at the right time, good sperm, quality egg, ideal uterine environment) and it still may not end in pregnancy.

Rainy34 Sun 01-Feb-15 16:54:35

purdie you should try your cbfm, Makes me feel more confident when we should be dtd

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