Mature follicles are 1.8-2.5 cm in size and can be monitored by ovulation test together with ultrasound. A strong positive ovulation test indicates a mature follicle and a weak positive test indicates a mature follicle. In case of regular menstruation, the 14th day before the next menstruation is the ovulation day. 5 days before and 4 days after the ovulation day, plus the ovulation day for a total of 10 days, is the ovulation period. During this period, the follicles will gradually develop and mature, and when they reach 1.8-2.5cm, ovulation will occur. Having intercourse within 24 hours before and after ovulation, the chance of pregnancy is high, reaching about 70%. You can also choose to have intercourse every other day during the ovulation period, so that there will always be viable sperm in the vagina, which will give you a higher chance of pregnancy.