[CG] Cervical length screening for women at risk of preterm labour


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Cervical length screening may be utilised to identify women at increased risk of preterm labour who may be candidates for preventative interventions. Data supporting the benefit of interventions is limited.

Cervical length can be measured between 16 and 24 weeks. For practical purposes, the majority of women who merit cervical length screening, this will be carried out at the 20 week fetal anomaly scan.  There may be women who require earlier cervical length screening or serial cervical length screening however in such cases this decision should be made by a Consultant Obstetrician.

This guideline does not address the role of cervical length measurements for women in threatened preterm labour.

The following women should be offered cervical length screening: 

  • Previous preterm birth <34+0 weeks
  • 2nd trimester loss where the cause is unclear
  • >1 LLETZ 
  • Cone biopsy/ Trachelectomy


The following women should NOT be offered cervical length screening routinely:

  • Multiple pregnancy
    At present there is no adequate clinical benefit to justify routine cervical length screening in this group of women.  Cervical length may be assessed in women recruited to the STOPPIT-2 study. However, in women being referred to Fetal Medicine for management of TTTS a cervical length measurement should be performed.
  • Following cervical stitch placement
    No proven clinical benefit of routine post-stitch cervical length measurement or surveillance

Management of results                        

≥25mm: No further action necessary

< 25mm: Refer to Obstetric Consultant. To be seen within 2 working days

<5mm or open: Refer to on call Obstetric Consultant for consideration of a rescue suture.


Treatment options

Counsel the woman that she is at an increased risk of preterm labour.  Discuss the benefits and risks of prophylactic progesterone, cervical stitch and conservative management with the woman taking her preferences into account as well as the clinical situation, past history and original reason for screening.

( Dosage : Prophylactic vaginal progesterone Cyclogest® 200mg vaginal suppository once daily)

Cervical stitch patient information leaflet (RCOG)

Last reviewed: 04 December 2018

Next review: 01 December 2023

Author(s): Dr Dawn Kernaghan (Consultant Obstetrician)

Approved By: Obstetric Guideline Group