Use of uterine electromyography to diagnose term and preterm labor

Abstract

Current methodologies to assess the process of labor, such as tocodynamometry or intrauterine pressure catheters, fetal fibronectin, cervical length measurement and digital cervical examination, have several major drawbacks. They only measure the onset of labor indirectly and do not detect cellular changes characteristic of true labor. Consequently, their predictive values for term or preterm delivery are poor. Uterine contractions are a result of the electrical activity within the myometrium. Measurement of uterine electromyography (EMG) has been shown to detect contractions as accurately as the currently used methods. In addition, changes in cell excitability and coupling required for effective contractions that lead to delivery are reflected in changes of several EMG parameters. Use of uterine EMG can help to identify patients in true labor better than any other method presently employed in the clinic.

© 2010 The Authors Acta Obstetricia et Gynecologica Scandinavica© 2010 Nordic Federation of Societies of Obstetrics and Gynecology.

Figures

Figure 1

Electrical activity of the myometrium (EMG activity; top trace) is responsible for uterine contractions. Note the excellent temporal correspondence between EMG and mechanical contractile events (measured by tocodynamometry; bottom trace). The numbers on the y-axis of the tocodynamometry trace are arbitrary units.

Figure 2

Electrode placement on the abdominal surface of the patient for performing uterine EMG measurement, to diagnose preterm and term labor.

Figure 3

Uterine EMG propagation velocity increases immediately prior to delivery (data shown for preterm patients). Open triangles, delivery ≤7 days from the measurement; and filled circles, delivery >7 days from the measurement.

Figure 4

Comparison of receiver-operating-characteristics curves for EMG parameters [power spectrum (PS) peak frequency and propagation velocity] vs. currently used methods to predict preterm delivery.

Figure 5

Illustration of the sample size calculation for two studies examining a hypothetical 10% effective treatment for preterm labor (PTL). In study 1, preterm labor is diagnosed by currently available methods. Consequently, 50% of patients included are not in true preterm labor and will not deliver preterm regardless of treatment. To demonstrate a 10% effect of treatment with an α of 0.05 and 0.80 power, 3129 patients would have to be included in study 1. If preterm labor were to be diagnosed by uterine electromyography (EMG; study 2), all the patients included would be in true preterm labor [positive predictive value (PPV) = 100%]. Only 147 patients would have to be included in this study to demonstrate the same efficacy with the same power.