1. A method for detecting an onset of true labor in a pregnant mammal, comprising the steps of: detecting electrical signals from a succession of muscular contractions associated with labor; determining an average frequency of the electrical signals occurring within a burst of electrical signals associated with a contraction; determining a discriminant (.delta.) from the determined average frequency for a plurality of contractions so as to provide a set of discriminants, individual ones of the set of discriminants being associated with an individual one of the contractions; and indicating a beginning of true labor when a slope of at least two discriminants of the set of discriminants exceeds a first threshold value and when a magnitude of a last determined discriminant exceeds a second threshold value.