Creatine kinase and its isoenzymes in the serum of women during pregnancy and the peripartum period.

In serum obtained from 28 women before, during, and after normal labor and delivery, creatine kinase activity was seen to be distinctly elevated immediately after labor and 24 h later, but had returned to normal six weeks later. In most cases the increase was due to the MM isoenzyme and was attributed to skeletal-muscle damage associated with labor. In 15 cases, the BB isoenzyme was observed, and in three patients the MB isoenzyme. Cord blood, which contains all three isoenzymes, may be the source of the MB and BB isoenzymes. Uterine muscle contains exclusively BB isoenzyme, and therefore uterine muscle damage is a likely source of the serum BB isoenzyme. The relationship among these isoenzymes in serum after delivery must be recognized, to avoid misdiagnosing myocardial infarction at this critical time.