Digital Ovulation Kits

Hi there, I'm looking at the ClearBlue Ovulation Tests & wondered whether anyone has tried them?

I've been pregnant twice before but unfortunately miscarried each time. We got pregnant after one month of trying last time, but now it's been about 5 months & no luck, so could do with some help in pinpointing my ovulation days.

Also, how soon in your cycle should you start using them?

Thanks!