• preimplantation factor;
  • lymphocyte/platelet binding assay;
  • early pregnancy test

PROBLEM: To evaluate the ability of the lymphocyte/platelet binding assay to identify a preimplantation factor (PIF).

METHOD: Percentages of binding of lymphocytes by platelets in the presence of sera from 30 known pregnant and 30 nonpregnant individuals were compared using a novel lymphocyte/platelet binding assay. The assay is performed using a combination of a heat inactivated sera with donor O+ lymphocytes, activated complement and an antibody against CD2(T11, Ortho Pharmaceuticals).

RESULTS: In nonpregnant females (23.6 ± 6.5%) and males (17.7 ± 4.7%) the percentage of lymphocytes bound by platelets was significantly different from pregnant women (56.1 ± 15.9%) (P < 0.0001). Serial sampling of blood in five women undergoing IVF/ET who had normal pregnancies showed the detection of PIF by 4 days after transfer. The lymphocyte/platelet binding assay was not influenced by hCG, progesterone and estradiol. The interassay and intraassay variabilities were <3%.

CONCLUSIONS: The lymphocyte/platelet binding assay is a simple, reproducible, specific and cost efficient assay for measurement of PIF. Application of this assay will provide investigative and diagnostic tools for identifying and monitoring early pregnancy events.