Objective: It is accepted now that most antiphospoholipid antibodies (APA) are not directed against phospholipids alone but complexes of phospholipid-binding proteins and phospholipids. One of the phospholipid-binding proteins is b2 -glycoprotein I (b2 -GPI), a normal plasma glycopro- tein, which under physiological conditions binds with negative charged phospholipids. Measure- ment of anti-b2 -GPI antibodies requires specific tests, since ELISA for determination of anticardiolipin antibodies (ACA) may detect both antibodies directly binding cardiolipin and antibodies against cardiolipin-binding proteins. In this study a comparison of APAs against cardi- olipin (CL), phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidylethanolamine (PE) v.s. anti-b2 -GPI were compared. Setting: First Institute of Medical Chemistry and Biochemistry, First Medical Faculty, Charles University and Institute for Care of Mother and Child. Design: Retrospective clinical study using stored sera for determination of APA. Methods: One hundred twenty four women in the first and the second trimester, who undergo biochemical prenatal screening for chromosomal disorders by maternal serum alpha-fetoprotein (MS AFP), human chorionic gonadotrophin (MS HCG) and trophoblast-specific b1 -glycoprotein (MS SP1) were studied. In serum samples antibodies against CL, PS, PE, PI (isotype IgG and IgM) were examined by solid ELISA. 19 women who were positive at least for one type of APAs were selected and in the serum samples the levels of anti-b2 -GPI were measured. Results: No pregnant woman with anti-b2 -GPI had positive antibodies against other phospholipids except CL. There was no significant correlation between levels of ACA IgG and IgM v.s. anti-b 2 - GPI IgG and IgM. Eight percent of serum samples were positive for both anti-b2 -GPI IgG and ACA IgG. In the second trimester a statistically significant decrease of ACA IgG was found (p = 0.014). The difference of ACA IgM and anti-b 2 -GPI IgG and IgM was not statistically significant. Levels of foetoplacental antigens in anti-b2 -GPI positive pregnant women were normal. Conclusion: A correlation between anti-b2 -GPI antibodies and ACA was not found in our study. Anti-b2 -GPI antibodies and ACA may be two different subpopulations of APA.

        Key words: antiphospholipid antibodies (APA), anti-b 2 -glycoprotein I antibodies (anti-b 2 -GPI), anti- cardiolipin antibody (ACA), biochemical prenatal screening