The cervix is the inferior, cylindrical portion of the uterus, approximately 3–4 cm in length, that projects into the upper vagina. Although small, it is one of the most clinically watched structures in obstetrics because cervical change is the most direct measure of labor progress and a critical determinant of whether induction will succeed. Throughout pregnancy the cervix functions as a mechanical and immunologic barrier, sealed by a mucus plug (operculum) that protects the uterine cavity from ascending infection. The cervix has distinct anatomical zones, each with its own epithelium: the ectocervix is covered by stratified squamous epithelium, the endocervical canal is lined by mucus-producing columnar epithelium, and the transformation zone (squamocolumnar junction) where the two meet is the site of most cervical dysplasia and cancer and the target of Pap testing. Why this matters clinically: During pregnancy the cervix softens (Goodell sign) and becomes more vascular, contributing to the bluish discoloration of the lower genital tract. As term approaches, the cervix ripens, transitioning from firm, long, and posterior to soft, effaced, and anterior under the influence of prostaglandins and...