A double bar measured on the ninth day of a frozen embryo transfer can be caused by a chorionic gonadotropin shot, or it can be caused by pregnancy. The chorionic gonadotropin shot is an injection that promotes ovulation, and early pregnancy tests are used to determine if a woman is pregnant by detecting this hormone in her urine. False-positive pregnancy tests can occur a relatively short time after the hormone injection because the drug has not yet been fully metabolized in the body, thus affecting the pregnancy test. If a woman detects a double bar on the ninth day of frozen embryo transfer, in order to rule out that it is caused by the chorionic gonadotropin injection, it is recommended to use the early pregnancy test paper again after about 12-14 days after the frozen embryo transfer, or carry out the blood HCG test to clarify whether she is pregnant or not. If the pregnant woman has abdominal pain and other symptoms, it is recommended to consult a doctor in time, under the guidance of the doctor, complete the relevant examinations to clarify whether the pregnancy.