Receiver operating characteristic (ROC) curve analysis of the relative efficacy of single and serial chorionic gonadotropin determinations in the early diagnosis of ectopic pregnancy.

A study was undertaken of 36 patients with viable intrauterine pregnancies who presented in the first trimester with abdominal pain and/or vaginal bleeding, and of 15 patients with ectopic pregnancies, all of whom had at least two human chorionic gonadotropin (hCG) determinations in the same gestation. The mean and lower 25%, 20%, 15%, 5%, and 1% limits of the rate of hCG increase in serum and of the serum hCG at different periods of gestation were determined for intrauterine pregnancy with the use of linear regression analysis, and each was used as a basis for identifying ectopic gestation. It was found that for any given false-positive rate, subnormal rates of hCG increase were more sensitive in identifying ectopic gestations than single "low for date" hCG values. It is suggested that the explanation for this may be that hCG production in many patients with ectopic pregnancies is normal until symptoms develop and falls thereafter as the functional trophoblastic mass is reduced by the shearing off the trophoblast from the tubal wall, which takes place with the development of the pregnancy and of symptoms.