Biological length scales in the human cervix. (A) The location of the uterine cervix based on segmentation of magnetic resonance imaging (MRI) data of a 20 week pregnant patient (Fernandez et al., 2015). (B) Collagen fiber directionality of an axial slice of a nonpregnant (NP) cervix imaged via optical coherence tomography (Gan et al., 2014). (C) NP cervical collagen fiber imaged via second harmonic generation (Myers et al., 2009). (D) NP cervical crosslink density (mole-per-mole basis with collagen) content, pyridinoline (PYD), deoxypyridinoline (DPD), dihydroxylysinonorleucine (DHLNL), pentosidine [PEN] (Zork et al., 2015).