How to distinguish between biochemical pregnancy and ectopic pregnancy

Biochemical pregnancy refers to the fertilized egg has been formed, but due to various reasons, the fertilized egg implantation failure, normal B ultrasound can not detect pregnancy. Ectopic pregnancy refers to the fertilized egg has been formed, but implanted in the outside of the endometrium, general abdominal color ultrasound examination can detect the fertilized egg outside the uterus.