Human chorionic gonadotropin testing for early pregnancy viability and complications.

Human chorionic gonadotropin (hCG) is a heterogeneous molecule that is the marker of choice for detecting pregnancy and indicating ectopic pregnancies and spontaneous abortions. This article describes the use of hCG in detecting pregnancy, and how pregnancy detection is complicated by the extreme variation in individual hCG results and by the varying structure of hCG. The problems of false-positive pregnancy tests due to early pregnancy losses or heterophilic antibodies, and of false-negative pregnancy tests due to delayed implantation, are discussed. Different kinds of pregnancy tests, professional laboratory assays, point-of-care, and home devices are compared. The use of hCG measurement and hCG doubling rates, progesterone measurements, and transvaginal ultrasound in identifying ectopic pregnancies and failing pregnancies also is reviewed.