Serum relaxin in patients with invasive mole, choriocarcinoma and persistent trophoblastic disease.

Human chorionic gonadotropin (hCG) is considered to be one of the factors which regulate relaxin secretion in humans. Serum immunoreactive relaxin levels are increased and are detectable by radioimmunoassay both in normal and molar pregnancy. Circulating hCG levels are increased in trophoblastic disease. In the present study, relaxin and hCG levels were sequentially measured in patients with invasive mole, choriocarcinoma and persistent trophoblastic disease. Serum relaxin levels were detectable by radioimmunoassay in these patients before treatment, though they were significantly lower than in normal pregnancy. The corpus luteum of pregnancy is the main source of circulating relaxin in normal pregnancy. The existence of a corpus luteum was confirmed in the 2 patients who underwent laparotomy. Consequently, the corpus luteum may also be the main source of circulating relaxin in trophoblastic disease. Parallel changes in hCG and relaxin levels were observed during the courses of trophoblastic disease. The finding suggests that relaxin secretion is dependent on hCG stimulation in trophoblastic disease in the presence of corpus luteum.