Preterm labor is a common obstetric complication. Clinical evaluation of cervical ripening to predict preterm labor is very inaccurate. 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 regular pregnancies. Optical properties of uterine cervices were measured in 13 patients at various time points of regular pregnancies. For each gestational trimester, mean values with 95% confidence intervals were calculated for oxy-, deoxy-, and total hemoglobin concentration (O(2)Hb, HHb, tHb), tissue oxygen saturation and water content and statistically significant differences between the trimesters were determined. The wavelength-dependent scattering (scatter power) was calculated by an exponential fit. O(2)Hb, and tHb and the scatter power showed an increase as a function of the gestational age. Differences between the second and the third trimester were statistically significant. HHb and the water content showed no significant change over time. Our results show that FD-NIRS is a promising diagnostic tool for providing information about cervical content of hemoglobin, water, and extracellular matrix proteins. We propose this technology to assess the cervical ripening and eventually to predict preterm labor.