A novel bioassay for detection of preimplantation factor (PIF)

To identify the presence of vital preimplantation embryos in vivo in humans, a newly observed phenomenon based on autorosette formation between lymphocytes and platelets, when treated with pregnant sera, was used as a marker.

Serum samples were obtained from 65 patients on the fourth day after embryo transfer (ET). Sera from 10 healthy males and 47 nonpregnant women were used as controls. The preimplantation factor (PIF) was detected by using blood group O+ donor lymphocytes and platelets incubated with blinded serum in the presence of anti-CD2 antibody and rabbit complement. Human chorion gonadotropin (hCG) concentrations were determined 7 days later and compared with results of the lymphocyte-platelets assay. Implantation was confirmed by ultrasonographic evidence of presence of an intrauterine gestational sac. The role of platelet activating factor (PAF) in the observed phenomena was studied experimentally.

Significantly more lymphocyte-platelet rosette formations were observed when sera from women who successfully implanted were compared to sera from women who failed to implant. This assay yielded a specificity of 95%, sensitivity of 88%, positive predictive value of 94%, and negative predictability of 90%. PAF added directly to the cell suspension and tested sera controls did not influence the percentage of lymphocyte/platelets rosettes.

The application of PIF assay will enable the identification and study of early pregnancy events before the implantation occur. PAF by itself is not responsible for the rosette formation.