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Cervical Os

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Updated July 02, 2014

Definition: the opening of the cervix. The cervical os dilates (opens) during childbirth to allow the passage of a baby. The cervical os can be further classified as internal os or external os.

  • External os: the opening of the ectocervix (lower part of the cervix that protrudes into the vagina)
  • Internal os: the part of the cervix closest to the main body of the uterus. The internal os is what the ob/gyn is referring to during pregnancy and childbirth when they speak of the os.
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