Leukocytes are consistently associated with degenerating embryos in IUD-bearing rhesus monkeys

Abstract

IN spite of intensive research during the past 15 yr the precise mechanism whereby an intrauterine device (IUD) exerts its contraceptive action is unclear. There is wide agreement that the effect is intra- rather than extrauterine, and is probably elicited after arrival of the conceptus in the uterine cavity and before its attachment to the endometrium¹. The most plausible suggestion seems to be that the device acts as a foreign body and provides a sterile inflammatory reaction in the endometrium which in some unknown way renders the uterine cavity hostile to preimplantation embryos^1,2. The presence of large numbers of inflammatory cells, consisting mainly of neutrophils and, to a lesser extent, macrophages, is a constant feature of the endometrial reaction in IUD-bearing women and other mammals. In some species there is a high positive correlation, in the presence of an IUD, between the concentration of leukocytes in the uterine fluid and the suppression of implantation (for example, in the rabbit³). So far, however, there has been no direct proof of a consistent association between leukocytes and unimplanted embryos in IUD-fitted primates. This paper provides evidence for such an association in the rhesus monkey.