Creatine kinase and its MB isoenzyme in the third trimester and the peripartum period.

Forty-nine normal pregnant women were recruited late in the third trimester for serial determinations of creatine kinase (CK) and its MB isoenzyme fraction (CK-MB) at four different times: (1) on recruitment between 36 and 40 weeks' gestation, (2) on admission in active labor, (3) immediately after delivery, and (4) on the first postpartum day. In the patients with vaginal delivery (n = 43) total CK was significantly elevated at time 4 compared with times 1, 2 and 3 (P value < .0001). CK-MB fraction was also significantly elevated at time 4 compared with times 1, 2 and 3 (P value < .0001). In 35.7% of the patients at time 4, CK-MB was sufficiently elevated to give the laboratory interpretation of "borderline" or "consistent with a myocardial infarction," even though none of the patients had cardiac symptoms or complications. A review of the literature shows that CK-MB is found not only in myocardium but also in uterus and placenta. The implication of this study is that elevations in total CK and CK-MB should be used with caution during the peripartum period to diagnose myocardial ischemia or infarction.