Some are more sensitive than other and measure 10 v's 25 (and I can not remember the units that it is measured in) so you might get a BFP on a Fortel Ultra on 13 DPO for example and a BFN on a Crystal Clear etc.
Chrissy,
Firstly, huge congratulations for your BFP - well done!!
Which brand of HPT did you find to be the best for your + result?
Also, I have a few more questions for you about preseed. If you have time, would you mind answering them in the Conception forum under the pre-seed topic posted by Flowerchild? Sorry to be a bother but I like to talk to those who have actually used the product for tips!
Hope you have a very sticky little one with a fab pregnancy to follow!!
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