A longitudinal study of cervical tissue composition changes during normal pregnancy in mice using spectroscopic photoacoustic

A sonographic short cervix is a major risk factor for spontaneous preterm birth (PTB). However, the cervical length is a suboptimal means to assess cervical status due to the lack of functional and molecular information. Spectroscopic photoacoustic (sPA) imaging is a non-invasive ultrasound-based technology for assessing cervical tissue compositions, such as collagen-to-water ratio (CWR), which are the major molecular changes during cervical ripening. A longitudinal CWR measurement by sPA was performed in murine cervices (n=3 per group) through the gestational ages from non-pregnant, 13.5 to 19.5 dpc, 6 to 12 hours, and 69 to 94 hours postpartum. The sPA data acquisition was performed in a range of wavelengths covering the peak absorption of collagen and water (1070to 1650 nm) with an amplified sPA wavelength unmixing method (sPA-CWR). The results indicated that the sPA-CWR method is capable of accurately quantifying cervical tissue composition changes during cervical remodeling. The non-pregnant murine cervical samples have significantly higher sPA-CWR than any other tissue group. A decrement in CWR at larger gestational ages was detected, which follows the cervical ripening process. In addition, the repair process was detected through increased CWR in tissue samples collected 6 to12 hours postpartum and completing their recovering process at about 69 to 94 hours postpartum. Finally, the imaging results were validated by quantitative histological analysis. These histological results confirm that the sPA-CWR measurements have a high correlation to the process of collagen reorganizing. Therefore, the sPA-CWR method can be a more accurate biomarker for estimating PTB risk.