Steinert's syndrome is a systemic disease with autosome mother-to-child transmission, characterized by myotonia and muscular dystrophia. The syndrome's clinical characteristics include: respiratory and alimentation diseases, facial diplegia, generalized hypotonia, areflexia, atrophy, arthrogryposis, hydramnios, retard in psychomotor development, cataract and genital disorders. A case of pregnancy occurs in Steinert syndrome's patient with hydramnios as a predominant symptom, is presented. At birth, in the congenital neonatal form, there is grave, generalized hypotonia which causes a very quick death of the newborn. There are not many characters which can be found out by ultrasound: hydramnios, reduction of fetal tone and active movements, micrognathia. Consequently it is of the utmost importance in those cases an adequate prenatal genetic counseling and a correct obstetrical management.