Whether pregnancy can be detected on the 13th day needs to be determined on a case-by-case basis. Generally, if you have intercourse during ovulation for about 10 days, you can use a pregnancy test or an early pregnancy test to detect whether you are pregnant. The ovulation date for women is usually about 14 days before the next menstrual period. The egg can survive in the fallopian tube for 1-2 days after it is discharged from the ovary and wait for fertilization, while the male sperm can maintain fertilization ability in the female reproductive tract for 2-3 days, so it is easier to conceive when having intercourse a few days before and after the egg is discharged. Usually the 5 days before and 4 days after the day of ovulation, together with the day of ovulation, totaling about 10 days, are collectively known as the ovulation period, when intercourse is more likely to result in conception. If you want to know the exact result, it is recommended to have a blood test at the hospital. If the value of HCG in the blood exceeds 20mIU/ml, it means that you are pregnant, if the value is between 0-5mIU/ml, it means that you are not pregnant.