Under normal circumstances, if the ovary is collecting one follicle, it requires estradiol to reach 200 pmol/L for successful ovulation. In most cases, estradiol is in the normal range of 200-1800 pmol/L at the time of ovulation. It is also clinically possible to know whether ovulation can occur by knowing the amount of estradiol. It is recommended that blood be drawn on the twelfth day of menstruation to check the level of estradiol to determine if ovulation will occur.