My ultrasound shows that i have a 17mm dominant follicle on cycle day 27. what does this mean? i usually ovulate on day 15.

2 possibilities: There are two possibilities: 1. It took you a lot longer to grow your dominant follicle this month. There are lots of things (stress) that can cause this. 2. What they are measuring as a follicle is really a simple cyst (they look very similar sometimes). If you get your menses on cycle day 29-30, then it was probably a cyst they saw. You can check a progesterone level a week after ovulation.