Unfortunately these tests didn’t provide accurate reflections of my progesterone levels. This past cycle, I had 3 of 4 negative Proov tests. I had gotten similar results for a few cycles before which caused me a lot of concern. Because of my prior negative tests and my concern I shared with my doctor, during this cycle, he ordered blood serum progesterone tests on days 6, 7 and 9 past peak. All tests were very positive (ranging from 16 to 26 ng/mL). I understand progesterone and PdG are different, but this tests is presented and marketed as a proxy for evaluating sufficient progesterone levels. Based on my blood tests, my levels were well above what would be sufficient and the alleged correlated 10 ng/mL of the Proov test. I think these tests may work well for some but my experience (and the feedback from my doctor when I asked him about the Proov test) was that this is not a reliable measure of progesterone or ovulation quality. I love data and would continue to utilize the strips if I could count on them correlating to accurate progesterone levels, but for me that was not the case. The customer service was very helpful though so it could be worth a try for you as long as you keep in mind the limitations and can keep your worry at bay until you get clinical blood work done in the event of negative tests.