Early Pregnancy Factor (EPF) was first described as a pregnancy-associated substance and its discovery created considerable interest as it enabled the detection of a potential pregnancy within 6 to 24 hours of fertilization in all pecies tested (e.g., mice, humans, pigs, sheep). Up to this time, it was considered that the embryo was a silent passenger during the preimplantation period and maternal recognition of pregnancy did not occur until implantation. With the discovery of EPF,it became apparent that the maternal system was preparing for implantation and successful pregnancy from the moment of fertilization. EPF is an immunosuppressant by virtue of its ability to release factors, which suppress a possible maternal immune response against the alien fetus.1
Early pregnancy factor in serum has been shown to be a marker of the presence of a viable embryo. In women the appearance of EPF has been reported within I - 2 days of coitus that resulted in pregnancy. In contrast, the earlest detectable concentration of beta-hCG human chorionic gonadotrophin) appears in maternal serum on day 8 following LH peak with most women producing detectable quantities on days 9 and 10 post LH peak. EPF remains in maternal circulation until about the last week of gestation but always disappears from serum before parturition.2
Before implantation, maternal serum EPF does not appear to be a product of the zygote (incorrectly referred to as a "fertilized egg") itself but of the maternal ovary in respose to a signal from the zygote, called ovum factor. Little is known about ovum factor as of now except that it has a relatively small molecular mass and is secreted by the ovum upon sperm penetration. Its production continues until the blastocyst stage of development.3
EPF can be bioassayed using the rosette inhibition test. EPF is expressed as rosette inhibition titer with values greater than 16 indicating a positive pregnancy. It must be understood that the rosette inhibition test embodies a complex cscade of events, which make it expensive to conduct, and the results somewhat difficult to interpret at times.4
Anti-EPF vaccines have been used experimentally. After fertile mating, mice were immunized with anti-EPF and when examined at autopsy at day 10, significant embryonic loss was noted.5 In a study done on a small group of IUD wearers, EPF became positive in half of the group and then disappeared, indicating the abortifacient activity of the IUD during the course of the implantation event.6
EPF is required very early in gestation for embryonic development. It is the earliest serum benchmark to date of positive fertilization and thus conception. Although the rosette inhibition test is costly and still in need of refinement, a study done on women using hormonal contraception would lay to rest once and for all the question of how often ovulation and conception occur and subsequently how often the demise of these pregnancies occur. As one would imagine, the pharmaceutical manufacturers who could afford such a study, are not interested in the information. Now that there is a clear marker available to be assayed, PFLI, Intl. (Pharmacists for Life International) is taking the initiative and insisting that such a study be undertaken in order that a clear and concise resolution to one of the most important questions of all time be resolved - how many abortions are caused by birth control pills.