In a pregnant woman at 18–24 weeks gestation with a cervical length ≤25 mm and no history of preterm birth, what is the appropriate management?

Management of Short Cervix (≤25 mm) at 18–24 Weeks Without Prior Preterm Birth

For a pregnant woman with a singleton gestation at 18–24 weeks with cervical length ≤25 mm and no history of preterm birth, prescribe vaginal progesterone, with the strength of recommendation depending on the exact cervical length measurement. 1

Diagnostic Confirmation

• Verify the measurement was obtained by transvaginal ultrasound using standardized technique (Perinatal Quality Foundation or Fetal Medicine Foundation protocols), as transabdominal measurements are insufficient for clinical decision-making 1, 2
• Ensure the bladder was empty during measurement and the cervix was visualized in its entirety 1

Treatment Algorithm Based on Cervical Length

Cervical Length ≤20 mm

• Prescribe vaginal progesterone immediately (GRADE 1A recommendation) to reduce preterm birth risk 1, 2
• This is the strongest evidence-based intervention available for this population 1

Cervical Length 21–25 mm

• Offer vaginal progesterone based on shared decision-making (GRADE 1B recommendation) 1, 2
• Discuss with the patient that the benefit is less certain than for cervical lengths ≤20 mm, but progesterone remains a reasonable option 2

Cervical Length >25 mm

• Expectant management with routine prenatal care 2

Interventions to AVOID

• Do NOT place cerclage in the absence of cervical dilation, even if cervical length is 10–25 mm (GRADE 1B recommendation against) 1, 2
• Do NOT prescribe 17-alpha hydroxyprogesterone caproate (17-OHPC), including compounded formulations (GRADE 1B recommendation against) 1, 2
• Do NOT place cervical pessary (GRADE 1B recommendation against) 1, 2

Critical Clinical Pitfalls

• Do not extrapolate these recommendations to twin pregnancies: vaginal progesterone, cerclage, and pessary are all ineffective in twins with short cervix and should not be used outside clinical trials 1, 3
• The 25 mm threshold is specific to singleton pregnancies without prior spontaneous preterm birth; different populations require different management strategies 1
• Cerclage in this population (no prior preterm birth, short cervix without dilation) shows no benefit and may cause harm 1, 2

Prognostic Information

• Transvaginal cervical length is one of the best available clinical predictors of spontaneous preterm birth, though sensitivity and positive predictive value remain modest in nulliparous women (8% and 16% respectively for predicting birth before 37 weeks) 1
• Risk of preterm birth increases progressively as cervical length decreases below 25 mm 4
• Short cervix is more predictive of early prematurity (<32 weeks) than later prematurity 4