A method for biasing sex selection, the method comprising the introduction into a uterus of a subject a volume of micro-particle conjugates (10), wherein the micro- particle conjugates are proportioned so as to approximate the size and shape of spermatozoa and thereby be carried by peristaltic waves through the uterus and fallopian tubes to the infundibulum, at which point any spermatozoa present or arriving thereafter undergo capacitation and expose antigens that may be bound by anti-male antibodies (14) provided in the micro-particle conjugates (10), the binding of the exposed antigens on the spermatozoa by the anti-male antibodies resulting in their inability to penetrate the Zona Pellucida of an egg and effect fertilisation.
