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.
