Contraindication of magnesium sulfate in a pregnancy complicated with late-onset diabetes mellitus and sensory deafness due to mitochondrial myopathy.

A primipara affected by late-onset diabetes and sensory deafness because of mitochondrial myopathy was hospitalized for threatened preterm delivery. Magnesium sulfate was started for tocolysis, resulting in general muscle damage, although the mitochondrial myopathy did not deteriorate during pregnancy. Magnesium sulfate may be contraindicated in pregnancy with mitochondrial myopathy.