Just thought I would post my experience here. I tested every day to check when Ovidrel would leave my system. I took Ovidrel two days prior to ovulation. You can see how it faded and then turned back to positive. I didn't have a pen handy so I used nail polish to mark the tests. Sorry!  Top is 6dpo, then 8dpo, then 9dpo, then 10dpo AM FMU and 10dpo PM. The First Response tests are 10dpo PM on the right and 11dpo on the left.  It was a true BFP, the first response without any writing on it was at 13dpo when my HCG was 58.