In vitro multifrequency electrical impedance measurements and modelling of the cervix in late pregnancy.

Idiopathic preterm labour is the greatest single perinatal problem occurring in an unpredictable 6-8% of all pregnancies and accounting for 75% of all perinatal deaths. Preterm cervical softening is used clinically as an important indicator of cervical dysfunction but the subjective nature of present clinical assessment methods prevents reliable prediction of preterm labour. This paper reports the finding of a pilot investigation concerned with obtaining quantitative measurements of the in vitro electrical impedance of the cervix using a four-electrode multifrequency impedance measurement system. Impedance measurement obtained from six samples of cervical tissue taken from different subjects of caesarean section were fitted to the Cole equation and parameters derived to describe the ratio of extra- versus intracellular impedance and the characteristic frequency. Subjects at term display a lower extra- versus intracellular impedance ratio than the preterm subjects. This appears consistent with the expected increase in the hydration of the cervix approaching term and the resulting decrease in the extracellular impedance. Further studies are required to determine if multifrequency electrical impedance tomography could be used as a non-invasive screening test for preterm labour.