A one-step diagnostic device for simultaneously detecting and distinguishing between a normal pregnancy and an ectopic pregnancy and methods for preparing the device are disclosed. Utilizing the device and principles of the present invention, normal pregnancy and ectopic pregnancy can be rapidly and accurately determined at an early stage by immunologically detecting the morphological differences between human chorionic gonadotropin (hCG) and modified forms thereof, which are secreted into the body fluid of a pregnant female.