Ectopic pregnancy. Diagnosis by sonography correlated with quantitative HCG levels.

Pelvic sonograms were correlated with simultaneous human chorionic gonadotropin (HCG) determinations in 150 women with early intrauterine pregnancy (N = 76) and ectopic pregnancy (N = 74). Of the 76 patients with intrauterine pregnancy (IUP), 55 had HCG levels exceeding 1,800 mIU/ml (Second International Standard), and in each case a gestational sac was identified. In comparison, 35 of 74 (47%) patients with ectopic pregnancy had HCG levels of 1,800 mIU/ml or more, and no case demonstrated a gestational sac. Although six patients (8%) with ectopic pregnancy demonstrated a "pseudogestational sac," no case was confused with a true gestational sac. We conclude that, when the HCG level exceeds 1,800 mIU/ml, an intrauterine gestational sac is normally detected and its absence is evidence for an ectopic pregnancy.