The follicular phase is 5-14 days of the menstrual cycle and ends on the day of ovulation when the follicular phase ends. 1-4 days is the menstrual phase, which manifests as menstruation due to the decrease in estrogen and progesterone levels, causing the discharge of the degenerated and necrotic endometrium mixed with blood. During the follicular phase, the primordial follicles in the ovary start to develop and last for about 10 days. 15-20 primordial follicles grow and develop and only one follicle matures and ovulation occurs, while the others form atretic follicles. The endometrium also starts to thicken, which is called the proliferative phase. At the end of the phase, ovulation occurs, also known as the pre-ovulatory phase, and the 15th day is the day of ovulation, and the chances of pregnancy increase when having intercourse 2-3 days before and after the day of ovulation. If you plan to get pregnant, you can have a pelvic ultrasound examination during the ovulation period to observe the development of the follicles and the thickness of the endometrium. If the follicles are developing normally, with a diameter of about 2cm and an endometrial thickness of about 8mm, you need to arrange intercourse in time.