Discriminatory hCG zone: its use in the sonographic evaluation for ectopic pregnancy.

TLDR

Ultrasonographic diagnosis of ectopic pregnancy depends on detecting an intrauterine sac after a positive pregnancy test, but this criterion requires knowing the hCG level at which a sac becomes visible, a threshold that is unknown for serum tests that detect pregnancy earlier than ultrasound. The study aimed to identify the hCG threshold that separates patients with visible intrauterine sacs from those without. The authors established this threshold, defining it as the discriminatory hCG zone. The discriminatory hCG zone lies between 6000 and 65000 mIU/ml; above this level, absence of an intrauterine sac indicates ectopic pregnancy, while below it, absence has no diagnostic significance, and a sac above the zone confirms intrauterine pregnancy, but a sac below the zone suggests an abnormal pregnancy such as missed abortion or ectopic gestation.

Abstract

The most reliable ultrasonographic criteria for diagnosing ectopic pregnancy are based on the appearance of the uterus in the presence of a positive urine pregnancy test. The absence of an intrauterine sac signifies ectopic pregnancy, whereas its presence indicates intrauterine gestation. These criteria cannot be applied when serum pregnancy tests are used unless the serum human chorionic gonadotropin (hCG) level at which the sac of an intrauterine pregnancy becomes visible on ultrasound is known, because these tests are far more sensitive and identify pregnancy at an earlier stage than does sonar. In this study, the hCG level that distinguishes patients with intrauterine pregnancies in whom a gestational sac can be seen from those in whom it cannot be seen was determined and designated the discriminatory hCG zone. This zone lies between 6000 and 65000 mIU/ml. The absence of an intrauterine sac in conjunction with hCG values above this level signifies ectopic pregnancy; however, the absence of an intrauterine sac has no diagnostic significance when associated with hCG values below the discriminatory zone. An intrauterine sac associated with hCG levels above the discriminatory zone reliably indicates an intrauterine pregnancy, but at hCG values below the zone, it is suggestive of an abnormal pregnancy-either a missed abortion or an ectopic gestation.