Measurement of cervical length

Curved cervix

The cervix is often curved and in these cases the measurement of cervical length taken as a straight line between the internal and external os is inevitably shorter than the measurement taken along the endocervical canal.

• From the clinical point of view the method of measurement is not important because when the cervix is short it is always straight.

Cervical funneling

Dilatation of the internal os, observed sonographically as funneling, is no more than a simple reflection of the process of producing cervical shortening that will eventually result in preterm birth. Almost all women with a short cervix have funneling of the internal os.

• Women with a long cervix and funneling are not at increased risk of preterm delivery.