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

Using an antiserum (H–93) specific to the COOH–terminal peptide of hCGβ 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.