FIELD: medicine. SUBSTANCE: the method deals with preventing undesirable pregnancy by intravaginal injecting efficient quantity of composition containing narrow- or monodisperse condensation polymer of aromatic sulfoacid and aldehyde, or its pharmaceutically acceptable salt. Moreover, it, also, deals with preventing undesirable pregnancy including vaginal introduction of gel containing the above-described condensation polymer. The innovation in question enables to apply the abovementioned compounds in manufacturing medicinal product to avoid pregnancy, or contraceptive preparation. By the present innovation these compounds either stimulate vagina poorly or do not stimulate it at all. EFFECT: higher efficiency. 9 cl, 27 ex, 2 tbl
