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Estimated mean log2 shear-wave speed of each region of interest of the external cervical os by continuous (4A), and categorical gestational age (4B). Figure 4C: adjustment for depth and cervical length for each region of the internal os in each of the gestational periods: I, <14 weeks; II, 14-<21 weeks; III, 21-<29 weeks; IV, 29 or more weeks.
