Background: Chest pain or discomfort are infrequent complaints among women during labor and early puerperium, but when present they raise the suspicion of myocardial ischemia. The diagnosis of the latter is based upon serum elevatIon of certain enzymes, such as aspartate amino transferase, lactate dehydrogenase and creatine phosphokinase. Nevertheless, the normal patterns of these enzymes in the serum during labor and early puerperium have not been characterized well.
Objective: To determine serum creatine phosphokinase, lactate dehydrogenase and aspartate amino transferase levels in late pregnancy, and throughout labor and early puerperium.
Methods: Fifty women having normal pregnancies followed by uneventful vaginal deliveries were prospectively studied for serum lactate dehydrogenase, aspartate amino transferase and creatine phosphokinase including its MB isoenzyme before, during and after labor. Cardiac status was evaluated in all women using serial electrocardiographic and physical examinations.
Results: All women were found to have low to normal antepartum serum enzymes levels. However, during labor total creatine phosphokinase increased markedly, reaching a peak of 2-4 fold baseline levels 24 hours postpartum. It then declined gradually back to baseline. Nulliparous women reached substantially higher levels than multiparous women. The MB or so-called cardio-specific isoenzyme was found to be an important contributor to creatine phosphokinase surge in most women. Correlation was demonstrated between length of the active phase of labor and both total and MB creatine phosphokinase activity. There was no clinical or electrocardiographic evidence for cardiac muscle damage in any of the study patients. Serum lactate dehydrogenase and aspartate amino transferase were not altered during or after labor.
Conclusions: Serum total creatine phosphokinase and its MB isoenzyme increase substantially during normal vaginal labor without evidence of myocardial ischemia. The uterus and placenta, two organs which were reported to embody substantial amounts of these enzymes, and which participate actively in the process of labor, are thought to release these enzymes to the circulation during labor. Knowing the normal patterns of these enzymes in the serum during labor and puerperium may prevent erroneous diagnoses of myocardial ischemia or infarction. Lack of electrocardiographic abnormalities and low lactate dehydrogenase and aspartate amino transferase levels may assist in excluding such diagnoses.