Pregnancy is well known to cause further progression of the clinical symptoms of Ménière’s disease. However, mild low-tone hearing loss and ear fullness, similar to the hearing impairment of Ménière’s disease, is often recognized in the ears of pregnant women who are not originally impaired. These phenomena seem to have a common backland to form endolymphatic hydrops. As to this background, various hypotheses have been proposed and developed. Hormonal changes and changes in body fluids due to pregnancy are considered in common to be based in these phenomena. In the present paper, theses hypotheses are reviewed.