I see this message was posted a while back - but I wanted to let anyone who might see this message (like I did) know that this advice might be very useful to someone in the situation the original poster described here.
I am right at 10 weeks pregnant, and decided to "double check" via a pregnancy test strip that I was still seeing similar results to what I was seeing earlier in my pregnancy. I had no particular concerns about miscarriage - I was just checking in. The pregnancy line in the test I took this morning was distinctly fainter than I had ever seen before (last strip I took was a few days ago). I hadn't had a distinct change in pregnancy symptoms recently, but I've had generally somewhat milder symptoms (to date) compared to what many others appear to experience. I am using bulk pregnancy strips purchased from Amazon, and followed the same procedure today that I had been following previously with these strips.
The faintness of the pregnancy line with respect to the control line was quite concerning to me. I had heard of needing to, in some cases, dilute the urine sample a little later in pregnancy when using home pregnancy tests - but in that moment I completely forgot about ever having heard of that effect. I began panic-Googling and came across this original post. I followed the advice listed here (10% urine sample, 90% water) and retook the test. The test strip exposed to the diluted sample returned a much darker pregnancy line than control line. The results were quick to develop.
I used a new strip to check the undiluted sample (in case strip from earlier in the morning had just been bad). Results were similar to earlier in the day - pregnancy line was much fainter than the control line.
Special thanks to the people who posted this thread discussing the need, at least in some circumstances, to dilute the sample. If you come across a similar situation, diluting the sample as described in this post might be worth trying.
Thank you so much for posting this information! In a moment of stress I completely forgot about this effect, and I am so grateful that I came across this post today. The authors of this information reduced a tremendous amount of pressure for me today, and I really do thank you.