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The cervix plays a crucial role in pregnancy and childbirth.
Indeed, the mechanical properties of the cervix change significantly as the gestational age of pregnant women increases.
In particular, during full-term gestation, the cervix undergoes a gradual softening up to 37 weeks of amenorrhea without substantial changes in its anatomy and mechanical strength, allowing the growing fetus to remain in the uterus.
This process accelerates after 37 weeks of amenorrhea, resulting in shortening and dilation of the cervix in preparation for delivery, which usually takes place around 41 weeks of amenorrhea.
The change in the mechanical properties of the cervix is due to a remodeling process of its microstructure involving connective tissue, one of the main microscopic components of which is collagen.
Several studies have shown that this process is due, among other things, to a decrease in the organization and density of collagen, as well as to an increase in its extractability and solubility.
Due to the lack of techniques to probe the microstructure of the cervix in vivo during pregnancy, the process of cervical remodeling remains poorly understood in full-term pregnancy and even more so in preterm delivery, which is the leading cause of perinatal mortality worldwide.
Several imaging techniques have been used to explore the microstructural changes of the cervix in pregnant women, such as X-ray, magnetic resonance, optical coherence tomography (OCT), and second harmonic generation (SHG).
However, the in vivo use of X-rays and magnetic resonance is limited due to their potential danger to the patient and the fetus.
In addition, OCT and SHG, despite their micrometric resolution, probe the cervical tissue with a small field of view and limited penetration depth, making these techniques difficult to use for in vivo applications.
In recent years, polarimetric imaging has shown great potential for exploring the structure of various types of biological tissues, including the cervix. In particular, this technique has shown great sensitivity in characterizing the density and organization of cervical collagen.
In this study, we used Mueller polarimetry to probe the cervical microstructure of pregnant women. The great advantage of this technique is that it can be performed with a macroscopic field of view, which is crucial for in vivo applications, while providing information on the microstructure of the tissue being explored. Furthermore, it has shown great promise in characterizing the density and orientation of cervical collagen.
We implemented this technique in vivo on a group of pregnant women at term. In particular, the anisotropy and scattering properties of the cervix have been characterized as a function of gestational age by measuring linear birefringence and total depolarization, respectively. The use of a multispectral approach allowed the characterization of these properties at different depths. The most relevant polarimetric parameters have been determined to monitor the remodeling of the cervical microstructure during pregnancy.
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