The role of routine cervical length screening in selected high- and low-risk women for preterm birth prevention

doi:10.1016/j.ajog.2016.04.027

American Journal of Obstetrics and Gynecology

Volume 215, Issue 3, September 2016, Pages B2-B7

https://doi.org/10.1016/j.ajog.2016.04.027 Get rights and content

Preterm birth remains a major cause of neonatal death and short and long-term disability in the US and across the world. The majority of preterm births are spontaneous and cervical length screening is one tool that can be utilized to identify women at increased risk who may be candidates for preventive interventions. The purpose of this document is to review the indications and rationale for cervical length screening to prevent preterm birth in various clinical scenarios. The Society for Maternal-Fetal Medicine recommends (1) routine transvaginal cervical length screening for women with singleton pregnancy and history of prior spontaneous preterm birth (GRADE 1A); (2) routine transvaginal cervical length screening not be performed for women with cervical cerclage, multiple gestation, preterm premature rupture of membranes, or placenta previa (GRADE 2B); (3) practitioners who decide to implement universal cervical length screening follow strict guidelines (GRADE 2B); (4) sonographers and/or practitioners receive specific training in the acquisition and interpretation of cervical imaging during pregnancy (GRADE 2B).

Section snippets

What is the clinical significance of a sonographically short cervix?

Women with a history of a prior spontaneous PTB account for only 10% of all births < 34 weeks of gestation.2, 3 Thus, researchers and clinicians have studied a variety of factors separate from past pregnancy history in order to further risk-stratify women and attempt to identify those at highest risk for PTB. Currently, mid-trimester CL assessment by transvaginal ultrasound is the best clinical predictor of spontaneous PTB.⁴ Depending on the population studied and the gestational age of

Should the cervical length be evaluated by transabdominal or transvaginal ultrasound?

Transvaginal ultrasound is considered the ‘gold standard’ measurement when assessing CL. In contrast to transabdominal ultrasound, transvaginal ultrasound measurements are highly reproducible, and measurements are unaffected by maternal obesity, cervical position, and shadowing from fetal parts.8, 9, 10, 11

Transvaginal ultrasound is also more sensitive than transabdominal ultrasound using CL cutoffs typically used to screen for a short cervix.¹² For example, the sensitivity using transabdominal

What steps should be performed to accurately evaluate the cervical length?

With the woman’s bladder emptied, the vaginal transducer should be inserted into the anterior fornix of the vagina and positioned so that the endocervical canal is visualized. The ultrasound probe should be gradually withdrawn until the image is just visible to ensure there is not excessive pressure on the probe. A minimum of 3 CL measurements should be obtained by placing calipers at the internal and external os. The shortest, best measurement should be recorded.16, 17, 18 (Box 1)

Ideally,

If the cervical length is assessed by ultrasound, when during pregnancy should it be evaluated?

If transvaginal CL screening is performed, the cervix should be assessed between 16 and 24 weeks gestation. It should not be routinely measured prior to 16 weeks of gestation.²¹ Prior to this time, the lower uterine segment is underdeveloped, making it challenging to distinguish this area from the endocervical canal. In fact studies evaluating first and early second trimester CL had not consistently shown adequate predictive value of CL measurement for preterm birth.22, 23, 24, 25

Routine CL

How should the approach to cervical length screening differ for women with and without a prior preterm birth?

The approach to CL screening varies based on patient characteristics and risk factors. Current SMFM and American College of Obstetricians and Gynecologists (ACOG) guidelines recommend women with a prior spontaneous PTB undergo CL screening with transvaginal ultrasound.10, 11 Serial assessment of CL is usually performed (every 1-2 weeks as determined by the clinical situation) from 16 until 24 weeks of gestation. We recommend routine transvaginal CL screening for women with singleton pregnancy

Should women with a history of treatment for cervical dysplasia (in the absence of a prior preterm birth) undergo routine serial cervical length screening?

There is insufficient evidence to support additional screening for women with a previous electrosurgical procedure (loop electrical excision procedure, LEEP) or cold knife cone for cervical dysplasia.

A recent large retrospective cohort study, as well as a systematic review and meta- analysis, found that while average CL is shorter in women after a procedure, most nevertheless have a normal mid-trimester CL and more importantly, the increased risk of spontaneous PTB in this population appears

Threatened preterm labor

Transvaginal ultrasound CL measurement may serve as an adjunct to digital cervical examination in the assessment of women with symptoms of acute PTL.51, 52, 53 Several observational studies have noted that the combination of CL and fetal fibronectin (FFN) assessment may improve prediction of PTB among women with symptoms of acute preterm labor.54, 55, 56 In triage units that combine CL screening and FFN testing in “symptomatic” patients, FFN does not add to PTB prediction in women with a very

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Cited by (179)

Differences in cervical length during the second trimester among normal weight, overweight and obese women: A systematic review and meta-analysis
2024, European Journal of Obstetrics and Gynecology and Reproductive Biology: X
Maternal obesity has been previously linked to increased risk of preterm birth; however, the actual pathophysiology behind this observation remains unknown. Cervical length seems to differentiate among overweight, obese and extremely obese patients, compared to normal weight women. However, to date the actual association between body mass index and cervical length remains unknown. In this systematic review, accumulated evidence is presented to help establish clinical implementations and research perspectives.
We searched Medline, Scopus, the Cochrane Central Register of Controlled Trials CENTRAL, Google Scholar, and Clinicaltrials.gov databases from inception till February 2023. Observational studies that reported on women undergone ultrasound assessment of their cervical length during pregnancy were included, when there was data regarding their body mass index. Statistical meta-analysis was performed with RStudio. The quality of the included studies was assessed using the Newcastle-Ottawa Quality Assessment Scale (NOS).
Overall, 20 studies were included in this systematic review and 12 in the meta-analysis. Compared to women with normal weight, underweight women were not associated with increased risk of CL < 15 mm or < 30 mm and their mean CL was comparable (MD −1.51; 95% CI −3.07, 0.05). Overweight women were found to have greater cervical length compared to women with normal weight (MD 1.87; 95% CI 0.52, 3.23) and had a lower risk of CL < 30 mm (OR 0.65; 95% CI 0.47, 0.90).
Further research into whether BMI is associated with cervical length in pregnant women is deemed necessary, with large, well-designed, prospective cohort studies with matched control group.
Universal cervical length screening: yes!
2024, American Journal of Obstetrics and Gynecology MFM
Universal cervical length screening and risk of spontaneous preterm birth: a systematic review and meta-analysis
2024, American Journal of Obstetrics and Gynecology MFM
To evaluate the risk of spontaneous preterm birth with or without universal transvaginal ultrasound cervical length screening at the time of midtrimester scan.
Medline, Embase, ClinicalTrials.gov, and Web of Science were systematically searched from the inception of the databases to November 12, 2023, using combinations of the relevant medical subject heading terms, key words, and word variants that were considered suitable for the topic.
Studies including individuals with singleton gestations at 16–25 weeks of gestation screened or not screened with universal transvaginal ultrasound cervical length screening were considered eligible. Primary outcome was spontaneous preterm birth <37 weeks; secondary outcomes were spontaneous preterm birth <34 and <32 weeks.
Random effect head-to-head analyses were used to directly compare each outcome, expressing the results as summary odds ratio and relative 95% confidence interval. The quality of the included studies was independently assessed by 2 reviewers, using the Newcastle-Ottawa scale for cohort studies and the Cochrane risk-of-bias tool for randomized controlled studies. The study was registered on the prospective register of systematic reviews database (PROSPERO) (registration number: CRD42022385325).
Eight studies, including 447,864 pregnancies, were included in the meta-analysis (213,064 screened with transvaginal ultrasound cervical length and 234,800 unscreened). In the overall analysis, universal transvaginal ultrasound cervical length did not significantly decrease the spontaneous preterm birth rates <37 weeks (odds ratio, 0.92 [95% confidence interval, 0.84–1.01], P=.07) and <34 weeks (odds ratio, 0.87 [95% confidence interval, 0.73–1.04], P=.12), but was significantly associated with a lower risk of spontaneous preterm birth <32 weeks (odds ratio, 0.84 [95% confidence interval, 0.76–0.94], P=.002). Individuals without a prior spontaneous preterm birth had a significantly lower risk of spontaneous preterm birth <37 weeks (odds ratio, 0.88 [95% confidence interval, 0.79–0.97], P=.01) and a lower trend of spontaneous preterm birth <32 weeks (odds ratio, 0.82 [95% confidence interval, 0.66–1.01], P=.06) when screened with transvaginal ultrasound cervical length, compared with no screening.
Universal transvaginal ultrasound cervical length screening usually <24 weeks in singletons without a prior spontaneous preterm birth, is associated with a significant reduction in spontaneous preterm birth <37 weeks, compared with no screening.
Randomized trial of screening for preterm birth in low-risk women - the preterm birth screening study
2024, American Journal of Obstetrics and Gynecology MFM
Preterm birth is a major cause of perinatal morbidity and mortality. It is unclear whether the introduction of a universal transvaginal ultrasound cervical length screening program in women at low risk for preterm delivery is associated with a reduction in the frequency of preterm birth.
To test the hypothesis that the introduction of a midtrimester universal transvaginal ultrasound cervical length screening program in asymptomatic singleton pregnancies without prior preterm delivery would reduce the rate of preterm birth at <37 weeks of gestation.
This study was a multicenter nonblinded randomized trial of screening of asymptomatic singleton pregnancies without prior spontaneous preterm birth, who were randomized to either cervical length screening program (ie, intervention group) or no screening (ie, control group). Participants were randomized at the time of their routine anatomy scan between 18 0/7 and 23 6/7 weeks of gestation. Women randomized in the screening group received cervical length measurement. Those who were found to have cervical length ≤25 mm were offered 200 mg vaginal progesterone daily along with cervical pessary. The primary outcome was preterm birth at <37 weeks. The risk of primary outcome was quantified by the relative risk with 95% confidence interval, and was based on the intention-to-screen principle.
A total of 1334 asymptomatic women with singleton pregnancies and without prior preterm birth, were included in the trial. Out of the 675 women randomized in the transvaginal ultrasound cervical length screening group, 13 (1.9%) were found to have transvaginal ultrasound cervical length ≤25 mm during the screening. Preterm birth at <37 weeks of gestation occurred in 48 women in the transvaginal ultrasound cervical length screening group (7.5%), and 54 women in the control group (8.7%) (relative risk, 0.86; 95% confidence interval, 0.59–1.25). Women randomized in the transvaginal ultrasound cervical length screening group had no significant differences in the incidence of preterm birth at less than 34, 32, 30, 28, and 24 weeks of gestation.
The introduction of a universal transvaginal ultrasound cervical length screening program at 18 0/6 to 23 6/7 weeks of gestation in singleton pregnancies without prior spontaneous preterm birth, with treatment for those with cervical length ≤25 mm, did not result in significant lower incidence of preterm delivery than the incidence without the screening program.
Contractions of the lower uterine segment during transvaginal ultrasound cervical length: incidence, significance, proper measurement, and management
2024, American Journal of Obstetrics and Gynecology MFM
An accurate transvaginal ultrasound cervical length is paramount to obtain the best prediction for preterm birth. Transvaginal ultrasound cervical length should be optimally obtained when a lower uterine segment contraction is not seen. For universal transvaginal ultrasound cervical length screening at approximately 20 weeks of gestation, the options are to do the transvaginal ultrasound soon after bladder void (lower uterine segment contractions present in 16%–43% of this approach) or to wait until the end of the anatomy scan (ideally within 30 minutes after bladder voiding) to decrease the chance of a lower uterine segment contraction. If the lower uterine segment contraction persists even after waiting up to 20 minutes or more, only the true transvaginal ultrasound cervical length should be reported. In particular, in patients with a previous spontaneous preterm birth, if the lower uterine segment contraction persists, the transvaginal ultrasound cervical length can be repeated in ≤7 days even in the presence of a normal (>25 mm) cervical length. Similar to a blood pressure cuff that must be of the right size for proper blood pressure measurement and a glucometer that must be properly calibrated, screening with transvaginal ultrasound cervical length should only be performed following a proper and standardized technique, including avoiding as much as feasible the presence of lower uterine segment contractions.
Ultrasonographic cervical length assessment in pregnancies with placenta previa and risk of perinatal adverse outcomes: a systematic review and meta-analysis
2024, American Journal of Obstetrics and Gynecology MFM
This study aimed to examine the association between cervical length and the risk of adverse outcomes in placenta previa pregnancies. In addition, the diagnostic accuracy of cervical length in predicting emergency cesarean delivery due to hemorrhage was evaluated.
PubMed, Web of Science, and Embase were systematically searched up to January 21, 2023.
Observational studies investigating the relationship between cervical length and maternal adverse outcomes in patients with placenta previa were considered eligible. The primary outcome was the diagnostic accuracy of cervical length measured at 28 to 34 weeks of gestation for the prediction of emergency cesarean delivery due to hemorrhage. The secondary outcomes were the probability of antenatal bleeding, preterm birth (both iatrogenic and spontaneous), and postpartum hemorrhage >2000 mL. Insufficient data were available on the transfusion procedure in cases where the cervical length was <30 mm.
For prognostic analysis, the random-effects model was used to pool the odds ratios and the corresponding 95% confidence intervals. For the diagnostic part, we used a summary receiver-operating characteristic curve, pooled sensitivities and specificities, area under the curve, and summary likelihood ratios.
A total of 13 studies presenting data on 1462 pregnancies with placenta previa were included. Cervical length ≤30 mm at 28 to 34 weeks of gestation had a sensitivity of 61% (95% confidence interval, 43–77), specificity of 83% (95% confidence interval, 76–88), and area under the curve of 0.83 (95% confidence interval, 0.80–0.86) for the prediction of emergency cesarean delivery. Furthermore, cervical length ≤30 mm was associated with antenatal bleeding (odds ratio, 3.62; 95% confidence interval, 2.09–6.26; P<.001; I²=54.8%), preterm birth (odds ratio, 8.46; 95% confidence interval, 3.05–23.44; P<.001; I²=83.6%), and postpartum hemorrhage (odds ratio, 6.89; 95% confidence interval, 4.51–10.53; P<.001; I²=0.00%).
Short cervical length (≤30 mm) measured at 28 to 34 weeks of gestation can assist in predicting the risk of emergency cesarean delivery due to hemorrhage in pregnancies with placenta previa. Furthermore, short cervical length is significantly associated with the risk of antenatal bleeding, preterm birth, and postpartum hemorrhage in pregnancies with placenta previa.

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: All authors and Committee members have filed a conflict of interest disclosure delineating personal, professional, and/or business interests that might be perceived as a real or potential conflict of interest in relation to this publication. Any conflicts have been resolved through a process approved by the Executive Board. The Society for Maternal-Fetal Medicine has neither solicited nor accepted any commercial involvement in the development of the content of this publication.

: This document has undergone an internal peer review through a multi-level committee process within the Society for Maternal Fetal Medicine (SMFM). This review involves critique and feedback from the SMFM Publications and Risk Management Committees and final approval by the SMFM Executive Committee. SMFM accepts sole responsibility for document content. SMFM publications do not undergo editorial and peer review by the American Journal of Obstetrics & Gynecology. The SMFM Publications Committee reviews publications every 18-24 months and issues updates as needed. Further details regarding SMFM Publications can be found at www.smfm.org/ publications. All questions or comments regarding the document should be referred to the SMFM Publications Committee. at [email protected].

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Society for Maternal-Fetal Medicine (SMFM) Consult Series | #40The role of routine cervical length screening in selected high- and low-risk women for preterm birth prevention

Section snippets

What is the clinical significance of a sonographically short cervix?

Should the cervical length be evaluated by transabdominal or transvaginal ultrasound?

What steps should be performed to accurately evaluate the cervical length?

If the cervical length is assessed by ultrasound, when during pregnancy should it be evaluated?

How should the approach to cervical length screening differ for women with and without a prior preterm birth?

Should women with a history of treatment for cervical dysplasia (in the absence of a prior preterm birth) undergo routine serial cervical length screening?

Threatened preterm labor

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Semin Perinatol

Am J Obstet Gynecol

BJOG

Semin Perinatol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Obstet Gynecol

Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Obstet Gynecol

J Obstet Gynaecol Can

J Obstet Gynaecol Can

Rates of and factors associated with recurrence of preterm delivery

JAMA

Prediction of patient-specific risk of early preterm delivery using maternal history and sonographic measurement of cervical length: a population-based prospective study

Ultrasound Obstet Gynecol

Cervical length at 23 weeks of gestation: prediction of spontaneous preterm delivery

Ultrasound Obstet Gynecol

Cervical length at 18-22 weeks of gestation for prediction of spontaneous preterm delivery in Hong Kong Chinese women

Ultrasound Obstet Gynecol

Society for Maternal-Fetal Medicine (SMFM) Consult Series | #40
The role of routine cervical length screening in selected high- and low-risk women for preterm birth prevention