Pregnancy is detected on the 15th day of ovulation as a result of late implantation, and ultrasound examination can be performed under the supervision of a doctor. Fertilization after ovulation is most often completed within 24 hours after ovulation, and the embryo settles in the uterine lining and begins to secrete HCG (human chorionic gonadotropin) 6 to 7 days after fertilization. Pregnancy can usually be detected through a blood pregnancy test about 10 days after intercourse during ovulation. So when pregnancy is not detected until the 15th day after ovulation, it is due to late implantation. In clinical practice, when pregnancy is confirmed by blood HCG test during early pregnancy, ultrasound is also performed to confirm intrauterine pregnancy as prescribed by the doctor. Since the embryo is late, the ultrasound can be performed 6 weeks after menopause to confirm intrauterine pregnancy and check the gestational week according to the size of the gestational sac and the size of the embryo buds. Folic acid should also be taken regularly during early pregnancy and follow-up prenatal checkups should be performed on time.