Soreness in the lower back and abdomen may occur after successful implantation, but there are individual variations. Generally, 6 to 7 days after fertilization of the sperm and the egg, the embryo will implant in the endometrium. During the process of implantation, a small number of pregnant women will experience bleeding during the implantation period, which may be accompanied by a slight sensation of soreness in the lower back and abdomen, which is a normal physiological phenomenon, but the majority of pregnant women do not experience these symptoms. Early pregnancy can be confirmed by testing blood HCG (human chorionic gonadotropin) levels at about 10 days after intercourse under the guidance of a doctor, and an ultrasound should be done at about 6 weeks after menopause to confirm intrauterine pregnancy. However, when abdominal pain, vaginal bleeding and a decrease in progesterone and blood HCG occur during early pregnancy, active fertility preservation treatment is required under the supervision of a doctor.