The normal cervix should have a length of 2.5cm or more from 10 weeks gestation until 36 week
The width of the cervical canal at the level of the internal os should be less than 4mm
Three measurements of the cervical canal length from the internal os to external os should be performed over three mintues. If there is significant curvature of the cervical canal a trace measurement or multiple measurements matching the curvature should be considered.
Evidence of funneling should be documented
Documentation:
Three cervical length measurments in the long axis