Gestational trophoblastic diseases: the ratio of choriogonadotropin to specific pregnancy protein, hCG/SP1, provides useful diagnostic and prognostic evidence.

Serum levels of human chorionic gonadotropin (hCG), specific pregnancy protein (SP1), and hPL were measured in 675 samples from women with uneventful pregnancy, and serially from the time of presentation in 125 patients with hydatidiform mole (HM), 43 with invasive mole (IM), and 34 with choriocarcinoma (CC). In HM serum levels of hCG and SP1 declined steadily from presentation to remission; when gestational age at the time of molar evacuation was shorter than 11 weeks, hCG declined to the normal range later than SP1 (57% patients), and when the age was longer--at the same rate as SP1 (26% patients) or earlier (17% patients). Serum levels of either marker were higher in IM than in HM and tended to increase, and in CC were either lower or higher than in IM. Treatment was followed by parallel decline of either marker, although SP1 declined to the normal range later than hCG in 12% of patients with IM and in 10% with CC. The hCG/SP1 ratios in normal pregnancy declined exponentially between the beginning and 23rd week of gestation and stayed level thereafter. The ratios calculated for the gestational age at the time of initial evacuation of the uterus or delivery were close to those of normal pregnancy in 80%, slightly increased in 20% of patients with spontaneously regressing HM, and markedly increased in 70% of patients with IM and in 74% of patients with CC. The ratios tended to increase during chemotherapy. An increase in the hCG/SP1 ratio seemed to be a characteristic sign of malignant change when compared with this ratio in normal pregnancy and hydatidiform mole. Determination of SP1 for monitoring therapy seemed redundant, and hPL assay was useful for discrimination between relapse and pregnancy.