In women with regular menstrual periods, pregnancy can usually be detected by ultrasound if the period is delayed for 15 days, but there are cases of late implantation in which the gestational sac is not visible on ultrasound. If your period is delayed and you have intercourse during ovulation, consider the possibility of pregnancy first. If your period has been delayed for 15 days, an ultrasound can detect pregnancy. If the pregnancy is intrauterine, the pregnancy sac can be detected by ultrasound. However, in the case of ectopic pregnancy, the gestational sac cannot be seen in the uterine cavity by ultrasound. Symptoms such as vaginal bleeding and tearing abdominal pain may occur. If a woman has regular menstrual periods, a blood test for HCG (human chorionic gonadotropin) 10-15 days after intercourse can confirm whether she is pregnant. Pay attention to rest in early pregnancy and take folic acid in the first trimester to prevent fetal cardiovascular malformation. If there is any discomfort, you need to go to the obstetrics and gynecology department of the hospital in time.