Ovulation usually occurs about 14 days before the next menstrual period. In women with regular menstruation and a 28-day menstrual cycle, menstruation begins around the 14th day after ovulation. During ovulation, the level of estrogen secretion reaches a peak of about 200 pg/mL and above. Estrogen stimulates the secretory function of the secretory cells, resulting in an increase in the secretion of cervical mucus, which is thin, transparent and can be stretched to more than 10 mm. At this time, the cervical mucus can be examined by smear, and after drying, leaf-like crystals of lambda plant can be seen. The cervical mucus is most suitable for sperm to pass during ovulation. After ovulation, due to the influence of progesterone, the mucus secretion gradually decreases, the mucus becomes viscous, the degree of drawing is poor, and it is easy to be broken. In clinical practice, the cervical mucus smear can sometimes be used to determine whether ovulation is occurring, so that the timing of intercourse can be guided to improve the chances of conception.