PROBLEM: Asymmetric IgG antibodies (AAb) possess a mannose-rich oligosaccharide residue bound to one of the Fab regions, making them unable to activate immunoeffector mechanisms. The proportion of asymmetric antibodies is increased after prolonged immunization with particulate antigens like cellular spleen cells. During pregnancy, AAb were found in serum and bound to placenta with specific activity to paternal antigens. No previous reports about the status of AAb in recurrent spontaneous abortion (RSA) patients have been published to date. Therefore, the aim of the present study was to analyze the percentage of asymmetric IgG molecules in serum samples of (a) healthy pregnant and non-pregnant women, (b) pregnant women with a history of RSA, and (c) non-pregnant RSA patients receiving paternal lymphocyte immunotherapy (LIT) or intravenous gammaglobulin therapy (IVIgs). METHOD OF STUDY: A previously-described differential ELISA technique was used to determine the percentage of IgG that was of the asymmetric type. RESULTS: During normal pregnancy, there was an increase in the percentage of high ConA affinity IgG serum molecules with a major increase at the second trimester. Pregnant RSA patients at the second trimester had lower values. When evaluating non-pregnant RSA patients who received LIT, it was observed that the immunized patients expressed a higher percentage of asymmetric IgG antibodies. The pregnant patients who received IVIgs had a percentage of AAbs comparable to normal pregnant patients. Additionally, the presence of IgG asymmetric molecules was confirmed in commercial gammaglobulin preparations. CONCLUSION: Results suggest a protective role of AAb during pregnancy.