Blood values are checked on day 14 of IVF transplantation and generally refer to the level of human chorionic gonadotropin (HCG) in the blood, which is at least more than 100 U/L but usually not more than 1,000 U/L. The day of transplantation is equivalent to the implantation of a pregnant egg. On the basis of a successful transplant, HCG begins to appear in the body from the day of transplantation and doubles every two days to 14 days when blood levels of the hormone exceed at least 100 U/L, but most do not exceed 1,000 U/L. A low blood level is considered a transfer failure, such as a failure of implantation similar to a biochemical pregnancy, or embryonic arrest, most often accompanied by vaginal bleeding. High values are associated with gestational trophoblastic disease, such as hyperemesis gravidarum. Normal range values indicate a high likelihood of successful in vitro fertilization, and may be followed up with ultrasound for 1 to 2 weeks to assess intrauterine embryo growth.