IN-VITRO MULTIFREQUENCY ELECTRICAL-IMPEDANCE MEASUREMENTS AND MODELING OF THE CERVIX IN LATE PREGNANCY

Idiopathic preterm labour is the greatest single perinatal problem occ urring in an unpredictable 6-8% of all pregnancies and accounting for 75% of all perinatal deaths. Preterm cervical softening is used clinic ally as an important indicator of cervical dysfunction but the subject ive nature of present clinical assessment methods prevents reliable pr ediction of preterm labour. This paper reports the finding of a pilot investigation concerned with obtaining quantitative measurements of th e in vitro electrical impedance of the cervix using a four-electrode m ultifrequency impedance measurement system. Impedance measurements obt ained from six samples of cervical tissue taken from different subject s at caesarean section were fitted to the Cole equation and parameters derived to describe the ratio of extra- versus intracellular impedanc e and the characteristic frequency. Subjects at term display a lower e xtra- 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 extrace llular impedance. Further studies are required to determine if multifr equency electrical impedance tomography could be used as a non-invasiv e screening test for preterm labour.