Thanks for the query.
In one cycle usually one dominant follicle will rupture and release ovum.
That is called as ovulation.
Presence of free fluid in pouch of Douglas is suggesting the ovulation.
Remaining follicles growth will be arrested.
If you are trying for pregnancy
, you have to plan intercourse around this period.
Without taking trigger also ovulation can occur naturally.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429