Just wanted to chime in with my Wondfo experiences. During my last clinical pregnancy, I used Wondfos and got a light but definitely visible line at 12dpo -- had a beta the next day and my HCG was 17, so it picked it up at a very low level. I actually also tested at 8dpo and 10dpo and had super light lines on those days as well but wrote them off. I continued testing until my HCG was at about 12,000 and it continued to get darker. I noticed it didn't get as dark as the control line until my HCG was in the hundreds, though.
Since that pregnancy, I've had Wondfos pick up several chemical pregnancies, too. They do seem very sensitive.
But! Here's something weird. An RE told me that he suspected some of my "chemical pregnancies" were actually LH surges being picked up by the HPTs. I honestly thought the man had no idea what he was talking about... I'd heard about OPKs picking up HCG, but not HPTs picking up LH. So I decided to test his theory... the next time I knew I was having an LH surge, I tested with a Wondfo HPT. Sure enough, I got a light positive, on 3 separate tests. I tested again after my LH surge was over, and the HPTs were negative.
So there you go. Wondfos are great at picking up low levels of HCG... and also high levels of LH!
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