A follicle of 18mm*19mm can be easily conceived within about 1-2 days of intercourse, and follicle development should be tested under the supervision of a doctor to guide intercourse. Normal follicles grow about 1.6mm per day, and before ovulation the follicle grows to about 20mm. When the follicle develops to 18*19mm by ultrasound monitoring, the follicle can be monitored every day or every other day, and it will usually ovulate within 1-2 days, so it is easy to conceive during intercourse within 1-2 days. However, there may be individual differences and intercourse can be guided under ultrasound monitoring. For pregnant women with regular menstrual cycles, ovulation occurs about 14 days before the next menstrual period, and 4-5 days before and after ovulation are easy to conceive, so it can be presumed that coitus during the ovulation period can improve the chances of conception under the guidance of the doctor. However, if your menstrual cycle is irregular, you can start monitoring follicular development on the 10th day of your menstrual cycle to guide your intercourse.