A study of uterine embryos recovered from rhesus monkeys fitted with intrauterine devices

Fifteen mature female rhesus monkeys were mated and operated upon to recover preimplantation uterine embryos. This resulted in the recovery of 25 embryos or unfertilized ava in 43 attempts. The same animals were fitted with plastic intrauterine devices (IUDs) and the recovery procedure was repeated. In this series 61 recovery attempts yielded only 10 embryos, 7 of which were sectioned and analyzed by transmission electron microscopy. This approach revealed the ultrastructural details of embryo degeneration and leukocyte association seen in embryos recovered from IUD-bearing animals. Samples of peripheral venous blood were analyzed for levels of ovarian steroids at the time of embryo recovery. The results are discussed in relation to the mechanism of action of IUDs.