Molar pregnancy in British Columbia: estimated incidence and postevacuation regression patterns of the beta subunit of human chorionic gonadotropin.

A total of 171 cases of molar pregnancy were followed by serial radioimmunoassay of the beta subunit of human chorionic gonadotropin (hCG-beta) over a 4-year period. The incidence over the study interval was 1:1,202 pregnancies in the province. In 120 women with intact uteri and measurable plasma levels of hCG-beta at the initiation of follow-up, the hormone remained detectable for up to 219 days (between 31 and 32 weeks) following evacuation, with 50% of patients remaining positive at 63 days (between 8 and 9 weeks). In five women undergoing hysterectomy, the hormone remained detectable for up to 112 days (between 15 and 16 weeks) postoperatively. In 92% of the cases, hCG-beta regressed to negative without chemotherapy. The prolonged presence of hCG in plasma after evacuation of the mole, regardless of the presence or absence of the uterus, points to persistence of molar tissue and its gradual rejection from uterine and extrauterine sites as a common phenomenon in the natural history of the uncomplicated postmolar course of this disease.