To determine the interval between your periods, count from the first day of one period to the first day of your next period. If you have a 28 day cycle, the first half of the cycle, days 1 through 14, is called the follicular phase. The second half, days 14 to 28 is the luteal phase. Your hypothalamus and pituitary glands, located in the brain, send messages through hormones to your ovaries and uterus. These follicles then release the hormone estrogen which causes the lining of the uterus to become thicker in preparation for pregnancy.
Pregnancy can occur if a sperm joins the egg and fertilization takes place.
For the next two weeks, the luteal phase of the cycle, the hormone progesterone further prepares the lining of the uterus for implantation of the fertilized egg. If pregnancy does not occur, then the progesterone level drops and bleeding begins around day 28. Not all women fit this 28 -day cycle, though most have fairly regular menstrual cycles. The interval from menstruation to ovulation can vary, but the time between ovulation and menstruation is the most consistent for all of us and is usually 14 days. If you are not ovulating, you cannot conceive.