Electrical impedance measurements of the uterine cervix in pregnancy
This is the first time that electrical impedance studies have been performed on the pregnant cervix. In this thesis the following has been demonstrated: 1. An inter-observer variability in resistivity readings, initially of the order of 20%, but decreasing to 1% once proficiency with the technique was established. 2. An intra-observer variability in resistivity readings of less than 15% in 94% of cases using the 5.5mm probe and 90% when using the 8mm probe. 3. A degree of heterogeneity in the pregnant cervix as attested to by the differences in resistivity measurements on different sites on the cervix. Some of these changes were partly due to technical difficulties. Nevertheless there appeared to be an increase in extracellular resistivity measurements between the anterior and posterior lips of the external cervical os. 4. A positive correlation between the resistivity measurements and gestational age using the 5.5mm probe. No significant correlations were identified between resistivity readings and both parity and maternal age. 5. A statistically significant difference in resistivity readings when comparing the non-pregnant and pregnant cervix. The change in readings was in a direction which reflected the increase in tissue hydration described by others. 6. A statistically significant difference between readings for ripe and unripe cervices at the time of induction of labour, with a fall in extracellular resistivity with increasing favourability as assessed by the Bishop score. This was accompanied by an increase in intracellular resistivity with increasing cervical favourability. The effect of prostaglandin administration on the pregnant cervix demonstrated a decrease in extracellular resistivity and an increase in intracellular resistivity associated with the cervical ripening process. Whilst the results were neither of statistical nor of clinical significance, they were nevertheless in the direction predicted. 7. A statistically significant correlation between extracellular resistivity and interval to delivery using the 8mm probe. 8. A new investigative modality that had high patient acceptability. To date the findings demonstrated in this thesis conceptually agree with the literature on the pregnant cervix. Thus it is imperative to continue with further studies of this new investigative modality.