Regular vacation refers to menstruation. On the 10th day of menstruation, the follicle is 2.1 centimeters, which indicates that the follicle has matured, and if you intend to get pregnant, you have a higher chance of getting pregnant at this time of intercourse. If you are not planning to get pregnant, you must use effective contraception. If your menstrual cycle is regular, ovarian ovulation usually occurs about 14 days before your next period. However, ovarian ovulation is also affected by many factors, such as environmental factors and mental factors, which may lead to early or delayed ovulation. An ultrasound on the 10th day of menstruation reveals that the follicle has grown to 2.1 centimeters, which means that the follicle has matured and may ovulate at any time. If you are planning to get pregnant, the chances of getting pregnant will increase significantly if you have intercourse at this time. If you are not planning to get pregnant, you need to take effective contraceptive measures, such as using condoms throughout.