When a woman reaches puberty, her ovaries mature and ovulation occurs cyclically. Normally only one follicle develops and matures per cycle, and each follicle contains one egg. To calculate the timing of ovulation, it is important to first distinguish between the following terms. Every month or so, the endometrium undergoes a collapse and shedding accompanied by bleeding, called menstruation. The first day of bleeding is called the first day of menstruation. The full course of bleeding is called the menstrual period. The menstrual cycle refers to the number of days between menstrual periods and is calculated from the first day of menstruation to the first day of the next menstrual period, according to WHO standards (guidelines). At the beginning of the menstrual cycle, the follicles grow in response to gonadotropins. As the follicles grow, the follicular fluid increases, while the size of the eggs does not change. The growing follicles gradually secrete estrogen, which peaks just before ovulation and stimulates the pituitary gland to release large amounts of luteinizing hormone, prompting the mature follicles to ovulate. Taking the usual menstrual cycle of 28 days as an example, ovulation occurs around the 11th to 16th day of the menstrual cycle. After ovulation, the ruptured follicles gradually form the corpus luteum and begin to secrete progesterone. Due to the combined effect of estrogen and progesterone, the endometrium is transformed into a secretory phase, creating conditions for the fertilized egg to be laid. Before and after ovulation, there can be some special signs, such as: 1. With the increase of estrogen level, the cervical mucus will become transparent and appear stretched, similar to egg white; some women also have breast swelling and pain. 2. At the time of follicle rupture some people will feel obvious lower abdominal pain, or have a small amount of ovulatory bleeding. 3. Due to the rise in progesterone after ovulation, it will lead to an increase in basal body temperature, about 0.5℃. 4. Using ovulation test strips to test the urine can also show the presence or absence of elevated luteinizing hormone. These can help women to determine whether they are in ovulation or not. However, these symptoms are only a reflection of possible elevated hormone levels in the body and are only an indirect reflection of ovulation. The most accurate method of ovulation monitoring is continuous ultrasound monitoring combined with hormone measurements.