Beta stands for beta hCG (human chorionic gonadotropin), which is produced by the embryo during pregnancy.  Serum levels of 5 IU/L or higher are a positive indication of pregnancy, and can be detected as early as two days after implantation.  A blood test for the presence of beta hCG is more sensitive, accurate and reliable than a home pregnancy test, the most sensitive of which can detect hCG in urine at levels of 20 IU/L or higher.