The ability to detect pregnancy before someone’s period is due to the fact that the fertilized egg begins to produce human chorionic gonadotropin before the next menstrual period. Fertilization usually occurs about 24 hours after ovulation, and it usually takes about 6-7 days for the fertilized egg to form and be planted in the uterine cavity. After the fertilized egg has settled, it begins to form human chorionic gonadotropin, or HCG, and as the pregnancy progresses, the amount of the hormone in the body of the pregnant woman increases, so that theoretically, a positive HCG test can be detected 7 days after ovulation, which means that she is pregnant. Ovulation usually occurs before the next menstrual period, and this period is usually 14 days, which is longer than the time it takes to detect HCG, so pregnancy can be detected before the onset of menstruation. Pregnant women should pay attention to the prenatal examination during pregnancy, actively listen to the advice of professional doctors to do a comprehensive nursing care, pay attention to rest, at the same time, should relax, avoid tension, anxiety, any discomfort should be timely to the hospital, the doctor to clarify the diagnosis, and cooperate with the doctor to deal with the symptoms.