What Causes The Follicle To Rupture Post A Miscarriage?

Hello doctor, I had a miscarriage a year before as i had bleeding and there was no heart beat for the baby at 12 weeks. I went to Gy and did a follicular study, My Left follicule was 16* 16 mm on Day 11 and iwas given a hcg Inj, 26*2mm on day 13 and 16mm endometrium on day 18. she said my follicule has ruptured and gave for 15 days and asked me to come after 15 days What the chances Please advice. Tnaks