But, “These kits are most reliable for women with regular, monthly menstrual cycles,” she notes. If you have irregular cycles, you may want to see a doctor to figure out why, since this can be an indicator of an underlying health issue. "The doctor can measure estradiol, [a form of the hormone estrogen], and LH levels in your blood" to determine when you're ovulating, Dr. Douglas explains. They also might do a trans-vaginal ultrasounds to track when the ovary that is going to release the egg, she says.