Abstract
Objectives
• To assess the association between sonography-derived cervical length measurement
and preterm birth.
• To describe the various techniques to measure cervical length using sonography.
• To review the natural history of the short cervix.
• To review the clinical uses, predictive ability, and utility of sonography-measured
short cervix.
Outcomes
Reduction in rates of prematurity and/or better identification of those at risk, as
well as possible prevention of unnecessary interventions.
Intended Users
Clinicians involved in the obstetrical management or cervical imaging of patients
at increased risk of a short cervix.
Target Population
Women at increased risk of a short cervix or at risk of preterm birth.
Evidence
Literature published up to June 2019 was retrieved through searches of PubMed and
the Cochrane Library using appropriate controlled vocabulary and key words (preterm
labour, ultrasound, cervix, cervical insufficiency, transvaginal, transperineal, cervical
length, fibronectin). Results were restricted to general and systematic reviews, randomized
controlled trials, controlled clinical trials, and observational studies. There were
no date or language restrictions. Grey (unpublished) literature was identified through
searching the websites of health technology assessment agencies, clinical practice
guideline collections, clinical trial registries, and national and international medical
specialty societies.
Values
The evidence and this guideline were reviewed by the Diagnostic Imaging Committee
of the Society of Obstetricians and Gynaecologists of Canada, and the recommendations
were made and graded according to the rankings of the Canadian Task Force on Preventive
Health Care (Online Appendix Table A1).
Benefits, Harms, Costs
Preterm birth is a leading cause of perinatal morbidity and mortality. Use of the
sonographic technique reviewed in this guideline may help identify women at risk of
preterm birth and, in some circumstances, lead to interventions that may reduce the
rate of preterm birth.
SUMMARY STATEMENTS (Canadian Task Force on Preventive Health Care grading in parentheses)
- 1In the general obstetrical population, cervical length is relatively stable over the first 2 trimesters. The natural history of cervical length change may not be useful in identifying women at increased risk of spontaneous preterm birth. Because there may be different patterns, rates, and/or onset of cervical length shortening, repeat assessment of cervical length may be useful in patients at high risk of spontaneous preterm birth (II-2).
- 2Transvaginal sonography can be used to assess the risk of preterm birth in women with a history of spontaneous preterm birth and to differentiate those at higher and lower risk of preterm delivery (II-2).
- 3Cervical length measurement can be used to identify those at increased risk of preterm birth in asymptomatic women at <24 weeks gestation who have other risk factors for preterm birth (uterine anomaly or prior multiple dilatation and evacuation procedures beyond 13 weeks gestation). However, there is insufficient evidence to recommend specific management strategies in this group of women (II-2).
- 4There is no consensus on the optimal timing or frequency of serial evaluations of cervical length. If repeat measurements are performed, they should be done at suitable intervals to minimize the likelihood of observation error (II-2).
- 5No specific randomized trials have evaluated any interventions in asymptomatic women initially diagnosed at or beyond 24 weeks gestation who are at increased risk of preterm birth (e.g., those who have a history of prior spontaneous preterm birth, uterine anomaly, or prior multiple dilatation and evacuation procedures beyond 13 weeks gestation) and who have a short cervical length. However, knowledge of cervicanalal length beyond 24 weeks may help with empiric management strategies for these women, such as relocation and increased surveillance (III).
- 6In women presenting with suspected preterm labour and intact membranes, transvaginal sonographic assessment of cervical length may be used to help stratify the risk of preterm delivery and prevent unnecessary intervention without harm. This information may result in a reduction in late preterm birth, but it is unclear whether it makes a significant clinical difference (II-2B).
- 7Cervical length surveillance is a safe option for patients with a prior sonography indicated cerclage, unclear history of cervical insufficiency, and prior spontaneous preterm birth when compared with routine cerclage based on clinical assessment; it may reduce the need for subsequent cerclage (II-2B).
- 8Transvaginal sonography appears to be safe in preterm prelabour rupture of membranes, but its clinical predictive value is uncertain in this context (II-2).
- 9There is insufficient evidence to support a committee position on the frequency or timing of sonographic cervical length assessment post cerclage. It is unclear if there is significant clinical benefit of such scans (III).
- 10Sonographic cervical length assessment and fetal fibronectin appear to be similar in predictive ability in symptomatic patients, and their combined value may not be significantly different from assessment of cervical length alone. More research is needed in this area (II-2).
RECOMMENDATIONS (Canadian Task Force on Preventive Health Care grading in parentheses)
- 1Transvaginal sonography is the preferred approach for cervical assessment to identify women at increased risk of spontaneous preterm birth, and it can be offered to women at increased risk of preterm birth (II-2B).
- 2Transperineal sonography can be offered to women at increased risk of preterm birth if transvaginal sonography is either unacceptable or unavailable (II-2B). Transabdominal assessment of cervical length may be a useful alternative for screening under certain conditions.
Keywords
Abbreviations:
LEEP (loop electrosurgical excision procedure), PPROM (preterm premature rupture of membranes)To read this article in full you will need to make a payment
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Article Info
Publication History
No. 401, December 2020 (Replaces No. 257, May 2011)
Footnotes
This document reflects emerging clinical and scientific advances as of the publication date and is subject to change. The information is not meant to dictate an exclusive course of treatment or procedure. Institutions are free to amend the recommendations. The SOGC suggests, however, that they adequately document any such amendments.
Informed Consent: Everyone has the right and responsibility to make informed decisions about their care together with their health care providers. In order to facilitate this, the SOGC recommends that they provide their patients with information and support that is evidence-based, culturally appropriate, and personalized.
Language and Inclusivity: This document uses gendered language in order to facilitate plain language writing but is meant to be inclusive of all individuals, including those who do not identify as a woman/female. The SOGC recognizes and respects the rights of all people for whom the information in this document may apply, including but not limited to transgender, non-binary, and intersex people. The SOGC encourages health care providers to engage in respectful conversation with their patients about their gender identity and preferred gender pronouns and to apply these guidelines in a way that is sensitive to each person's needs.
Copyright: The contents of this document cannot be reproduced in any form, in whole or in part, without prior written permission of the publisher of the Journal of Obstetrics and Gynaecology Canada.
Identification
Copyright
© 2020 The Society of Obstetricians and Gynaecologists of Canada/La Société des obstétriciens et gynécologues du Canada. Published by Elsevier Inc.
