Okay, very important to read this...
I was 7 weeks pregnant and using them to test my HCG. (I was out of the country and couldn't do the regular blood tests or ultrasound.) they started getting lighter than weeks 5 and 6 and I freaked out. turns out these tests can't handle that much HCG - by then I was likely at 25k-50k. It's called a hook effect. You can google it. Not many people are aware of it.
Interestingly, I learned to dilute my urine - put about 1/4 inch in a cup, then watered it down, dumped out half, watered it down again until it looked like pure water and it came out VERY DARK. It seems to only be able to read so much HCG before it's overloaded. At 10 weeks, I could dilute it 50-100x and still get a dark line!
Wondfos are fantastic. I've used them for years. sadly, they seem to be disappearing off the market but I've been using other brands that are $.20 each or so from the internet and they work just as well.
Hope that clears up why the 8 weeks were coming out light. And HCG peaks at about 10-12 weeks and then starts to drop but even after that, you will likely have to dilute it a lot to get an accurate DARK positive.
I've heard where women 4-6 months along were getting negatives from too much HCG.
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