The average cervical length varies with gestational age, measuring around 40mm at 20 weeks and approximately 34mm at 34 weeks.

When the cervical length measures less than 25mm, it is classified as a short cervix.

A cervical length of less than 15mm at 22-24 weeks gestation is very abnormal and is significantly associated with the risk of preterm birth.

Cervical screening may be necessary in the following situations:

• History of very preterm birth

• Previous cervical surgery (e.g., cervical cone biopsy/LLETZ procedure)

• Women with a cervical suture

• Suspected cervical incompetence

• Multiple pregnancies

To assess cervical length during pregnancy, a transvaginal ultrasound examination is necessary for an accurate measurement. It's important to ensure that the bladder is empty during the procedure. Additionally, there are no known risks associated with transvaginal ultrasound assessments in pregnancy.

The features assessed in cervical screening include:

• Length of the cervix (typically >25mm)

• Funnelling of the membranes into the cervical canal

• Dilatation of the cervix

• Location of a cervical suture (if present)

If the cervix is shortened to a very short length (< 25 mm) or is dilated during pregnancy, it is considered abnormal and indicates an elevated risk of preterm birth. In such cases, your obstetrician may consider implementing measures such as modifying activity, recommending bed rest, suggesting hospitalization, prescribing medications, or potentially recommending a cervical suture, based on the findings of the cervical screening and your individual situation.