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2. Recording of the Fetal Electrocardiogram;Ward;Am. Heart J.,1942
3. Fetal Electrocardiograms of the Human Subject;Maekawa;Acta scholae med. univ. imp. in Kioto,1930
4. Human Foetal Electrocardiogram;Bell;J. Obst. & Gynaec. Brit. Emp.,1938
5. A Clinical Evaluation of Fetal Electrocardiography;Bernstein;Am. J. Obst. & Gynec.,1942