Hormone involvement in the establishment of pregnancy

Introduction The capacity of the conceptus to synthesize a variety of hormones has been established for many years (Klopper & Diczfalusy, 1969; Davies & Ryan, 1972; Fuchs & Klopper, 1977). It has been demonstrated that the embryo is able to influence maternal functions before and during the implantation or attachment period (De Feo, 1967; Heald, 1976; Perry, Heap, Burton & Gadsby, 1976) although the means by which it secures its continued existence and development at this time are only now becoming clear. The objective of this review is to discuss aspects of embryonic and uterine development during the pre- and peri-implantation period in relation to the hormonal exchanges believed to occur at this time. The main emphasis is placed on embryonic hormones, particularly steroids, in relation to the influence of hormones on preimplantation embryonic development, maternal recognition of pregnancy and hormonal involvement in the implantation process.