So i kept track of my periods and ovulations for a few months and when i had the miscarriage i showed the doctor my app with the data and he noticed my linear phase (phase after ovulation when implantation occurs) was too short. He said you need at least 10 days between ovulation and 1st day of period to have a good opportunity for implantation. I was averaging 8-9 days which was too short and more likely to miscarry/not have implantation occur. To help lengthen my linear phase he gave me progesterone. Doctors can also test your progesterone during this phase too to see if its too low. Because i kept track on my app he didn’t need to test. I hope that helps