Absence of hCG-like activity in the blood of women fitted with intra-uterine contraceptive devices.

Blood was obtained at various stages of the menstrual cycle from 201 women fitted with intra-uterine contraceptive devices (IUDs), and plasma levels of hCG were determined by radioimmunoassay. Urine samples were obtained from 117 of these women and tested, before and after sephadex gel filtration, in a haemagglutination inhibition test for pregnancy (Pregnosticon). Plasma hCG was undetectable (less than 25 MLU/ml) in all but one of the 201 women and, in this instance, the hCG-assay appeared to be measuring a midcycle peak of LH, as evidenced by high plasma FSH levels. All unextracted urines gave negative results in the Pregnosticon test but, after extraction, 18 of the 117 urines gave positive reactions, most of these being from women at midcycle or in the luteal phase. We conclude that the IUD does not permit the development of the embryo to a point where it is capable of secreting measurable amounts of hCG. Recent claims to the contrary are probably due to cross-reaction of LH or non-specific interference in the assays used for measuring hCG.