One to five transvaginal ultrasound scans were taken of 63 women to estimate the microstructural changes in cervix using ultrasonic attenuation. Spectral log difference algorithm showed a clear decrease in attenuation as the time to delivery comes closer. The decrease in attenuation occurs earlier in preterm birth compared to full term birth which can be used as a predictor for preterm birth. Attenuation estimate did not improve as the ROI size increased.