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The Role of Routine Cervical Length Screening For Preterm Birth Prevention

CLINICAL ACTIONS:

Professional organizations have released guidance on cervical length (CL) screening for preterm birth (PTB) prevention. The finding of a short cervix, irrespective of obstetric history, has been consistently shown to be associated with higher risk for PTB.

Steps for CL assessment

  • Have patient empty bladder
  • Acquire the sagittal, long-axis image of entire cervix (75% of screen)
  • Confirm that the anterior and posterior cervixes are of equal thickness
  • Measure endocervical canal from internal to external os
    • Ensure that internal and external os are seen and canal seen throughout
    • Place calipers at the internal and external os where the anterior and posterior walls of the cervix meet
  • If the endocervical canal curves
    • Add linear measurements together to obtain the final cervical length
  • Dynamic cervical shortening
    • Exam time 3–5 minutes and/or
    • suprapubic/fundal pressure
  • Obtain 3 images for CL determination
    • Use the shortest, best measurement

Who and When to Screen for CL

Screening in Asymptomatic women

  • ACOG
    • Uncertainty regarding clinical utility of endovaginal cervical length screening
      • Incidental finding of short cervix is associated with increased risk and vaginal progesterone may be of benefit 
    • Cervix should be visualized as part of 18w0d to 22w6d anatomy scan using either abdominal or endovaginal approach 
    • If a short cervix is found on abdominal scan, endovaginal ultrasonography is recommended
  • SOGC (Canada)
    • Universal screening in Canada can not be mandated at this time and more research is warranted
  • ISUOG
    • CL measurements should be done by transvaginal scanning that would require additional consent, appropriate training and result auditing 
    • Based on the above, “CL measurement can be carried out meeting these conditions, it can be considered as an integral part of the routine mid-trimester scan”
  • RANZCOG
    • Cervical length measurement at 18-24 weeks should be “considered”
    • Two step approach of abdominal scan first followed by transvaginal as needed
  • FIGO
    • Does recommend measurement in low risk population
    • “Should be performed in all pregnant women at 19–23+6 weeks of gestation using transvaginal ultrasound”
    • Can be done same time as anatomic scan

Surveillance in asymptomatic women with prior sPTB

  • ACOG: Every 1 to 4 weeks (depending on clinical status) between 16w0d and 24w0d 

SYNOPSIS:

Two thirds of preterm births are spontaneous, and only 10% of births <34 weeks will occur to women with a history of spontaneous preterm birth (sPTB). Few predictive tests are available for PTB prediction, and mid-trimester CL assessment remains the best clinical tool at identifying high-risk women. Women with short cervix and prior sPTB are at highest risk.

KEY POINTS:

  • If cervical length is 25 mm or less
    • “Options for intervention include cerclage or vaginal progesterone”
  • Transvaginal ultrasound is more sensitive and reproducible that transabdominal ultrasound in detecting cervical shortening
  • Sonographers and practitioners should receive specific training in acquisition and interpretation of cervical imaging

Special circumstances

  • History of treatment for cervical dysplasia (LEEP, cold-knife cone)
    • Observational data inconsistent
    • Risk may be increased if excision greater than 15 mm in depth and short time between surgery and pregnancy 
  • Multiple gestations
    • ACOG does not recommend CL surveillance due to lack of effective interventions
    • As with average risk population, if short cervix found on transabdominal ultrasound, proceed to endovaginal ultrasound 

Learn More – Primary Sources:

ACOG Practice Bulletin 234: Prediction and Prevention of Spontaneous Preterm Birth

ISUOG Practice Guidelines (Updated): Performance of the routine mid-trimester fetal ultrasound scan

Fetal Medicine Foundation Cervical Length Assessment Program

SOGC: Universal Cervical Length Screening

FIGO: Best Practices in Maternal Fetal Medicine 

ISUOG: How to Measure Cervical Length

Cervical Cerclage – Professional Recommendations

CLINICAL ACTIONS:

ACOG defines cervical insufficiency as “the inability of the uterine cervix to retain a pregnancy in the absence of the signs and symptoms of clinical contractions, or labor, or both in the second trimester.” In addition, ACOG separates out indication for cerclage in to 3 categories

  • History: ≥1 of the following
    • Second trimester pregnancy losses related to painless cervical dilation and no history of labor or abruption
    • Previous second trimester cerclage for painless cervical dilation
  • Physical Examination: Also known as ‘physical examination–indicated cerclage’, ‘rescue cerclage’ and ’emergency cerclage’
    • Patient presents with painless second trimester cervical dilation
  • Ultrasound: Cervical length shortening and history of preterm birth
    • Singleton pregnancy
    • Prior spontaneous preterm birth (<34 weeks)
    • Cervical length:  <25 mm (at <24 weeks)

Timing of Cerclage Placement

  • History-indicated cerclage
    • Place between 12 and 14 weeks after confirmation of pregnancy viability
  • Ultrasound or exam-indicated cerclage
    • May be placed prior to 23 weeks

Risk Factors

  • Prior PTB
  • Repeated cervical dilation
  • Cervical procedures (including cone and LEEP)
  • Cervical laceration
  • Urogenital abnormalities

SYNOPSIS:

Clinically, cervical insufficiency is painless dilation and recurrent mid-trimester losses without signs of preterm labor (PTL), PPROM, or infection. Patient history may include superimposed symptoms (i.e. bleeding, pressure), therefore a judicious review of records is advised.  Those with a history of prior preterm birth can benefit from cervical length screening to appropriate guide selected patients for cerclage.

KEY POINTS:

Ultrasound Indicated Cerclage with Prior History of Preterm Birth <34 weeks and cervical length <25 mm before 24 weeks  

  • Cerclage associated with
    • Decreased preterm birth 
    • Improved neonatal outcomes  
  • No history of preterm birth
    • Cerclage for short cervix at <24 weeks has not been associated with improved preterm birth rates    
  • Evidence from research studies
    • There is no demonstrated difference in efficacy of McDonald versus Shirodkar techniques
  •  

‘Emergency’ Cerclage (Exam indicated)

  • There is literature, including a meta-analysis (Obstet Gynecol, 2015), to support ’emergency’ or ‘rescue’ cerclage
    • Neonatal survival
      • Cerclage: 71% survival
      • No cerclage: 43% survival
      • Relative risk 1.65 (95% CI 1.19 to 2.28)
    • Prolongation of pregnancy
      • Mean difference: 33.98 days (95% CI, 17.88 to 50.08)
    • Authors note significant limitations including quality of data and only 1 RCT included

After clinical examination to rule out uterine activity, or intraamniotic infection, or both, physical examination-indicated cerclage placement (if technically feasible) in patients with singleton gestations who have cervical change of the internal os may be beneficial

Additional Interventions

  • Evidence does not support use of the following after cerclage placement
    • Serial cervical length measurements
    • Antibiotics
    • Prophylactic tocolysis

Cerclage Removal

  • Remove transvaginal McDonald cerclage at 36 to 37 weeks
  • Cesarean delivery planned for ≥39 weeks
    • May be removed at time of delivery
    • Consider possibility of spontaneous labor between 37 and 39 weeks
  • McDonald cerclage may be removed in the office
  • PPROM
    • Removal or retention “is reasonable”
    • Prolonged antibiotic prophylaxis >7 days not recommended if suture is retained
  • Preterm labor
    • Diagnosis may be more difficult with cerclage in place

Routine management of preterm labor should be followed for patients with symptomatic preterm labor

If cervical change, painful contractions, or vaginal bleeding progress, cerclage removal is recommended

Learn More – Primary Sources:

ACOG Practice Bulletin 142: Cerclage for the Management of Cervical Insufficiency

Physical Examination–Indicated Cerclage: A Systematic Review and Meta-analysis