Transitory hCG-like activity in the urine of some IUD users

Using an antiserum (H-93) specific to the COOH-terminal peptide of hCG beta and gel chromatography, we found the transitory (1-2 days) presence of a gonadotropin having immunological, biological, and physical similarity to hCG, but not typical hLH, in the late luteal phase (days 24-29) urine of some (5 of 26) IUD users. We did not detect hCG in sera from any of the women. Although the source of the hCG-like gonadotropin is unknown, the data suggest that late luteal phase implantation may have occurred transiently.