1. The model is divided into six parts.
2. The cervix has not dilated, and the cervical canal has not disappeared;
3. The cervix dilates by 2 cm, and the cervical canal disappears by 50%;
4. The cervical opening dilates by 2 cm, and the cervical canal disappears completely;
5. The cervical opening is expanded by 5 cm, and the cervical canal disappears completely;
6. The cervix dilates 7 cm, and the cervical canal disappears completely;
7. The cervix dilates by 9 cm, and the cervical canal disappears completely.