Frequency domain near-infrared spectroscopy of the uterine cervix during cervical ripening.

Objective: Preterm labor is a common obstetric complication. Clinical evaluation of cervical ripening to predict preterm labor has a substantial inter- and intraobserver variability. We used frequency domain near-infrared spectroscopy (FD-NIRS) to non-invasively investigate the changes of the optical properties (i.e., absorption and scattering of light) in the uterine cervix during drug-induced cervical ripening.

Methods: Ten volunteers scheduled for abortion were examined. Optical properties of the uterine cervix were measured and physiological parameters were calculated prior to and after induction of cervical ripening using topical misoprostol. Mean relative changes, +/-standard error of the mean as well as statistical significance using the t-test were calculated for oxy- and deoxyhemoglobin, total hemoglobin, oxygen-saturation, and water. The wavelength-dependent decrease of scattering (scatter power) was calculated by an exponential fit and tested with the Wilcoxon test.

Results: Misoprostol induced a decrease in total hemoglobin of 21 +/- 6% (P < 0.05), a decrease in oxyhemoglobin of 22 +/- 6% (P < 0.05), a decrease in deoxyhemoglobin of 16 +/- 11% and an increase of 36 +/- 8% (P < 0.005) in water content. The scatter power was significantly lower (P < 0.05) after cervical ripening.

Conclusion: Our results show that FD-NIRS is a promising diagnostic tool to detect changes in cervical concentrations of hemoglobin and water. A severe tissue edema, probably due to a hormone-induced inflammatory process, seems to be important for cervical ripening. The reduction in total hemoglobin is likely to be a consequence of the increased water content of the tissue resulting in a dramatic increase of the distance between vessels. We propose this technology to assess the cervical ripening and eventually to predict preterm labor.