['To evaluate the ability of preimplantation factor (PIF) measured in the lymphocyte/platelet binding assay (LPBA) to predict subsequent spontaneous abortion.', 'Serum from 57 women experiencing first trimester pregnancy losses were studied using the LPBA (46 women conceived after in vitro fertilization and embryo transfer for treatment of infertility and 11 with a history of unexplained recurrent spontaneous abortion conceived spontaneously). The assay employs a combination of heat inactivated sera with donor O+ lymphocytes and platelets, complement and an antibody against CD2. Chromosome analysis was performed on 32 of the abortuses. Results of PIF assay were compared between karyotypically normal and abnormal abortuses.', 'PIF assay was negative in all 57 women at the time of abortion. Among 12 karyotypically normal abortuses only 1 woman (8%) had an initial positive PIF, 11 (92%) had negative PIF. Serial PIF assays were performed on 15 women. PIF assay became negative a minimum of two weeks prior to demonstration of intrauterine demise at a time when hCG concentrations remained elevated. A trend to subnormal was seen in women with normal when compared to those with abnormal abortus karyotype, but the numbers were too small to reach statistical significance (P = 0.09).'] Does preimplantation factor ( PIF ) predict subsequent pregnancy loss?