What is the next step in management for a 24-week pregnant woman with a cervical length of 27 mm on transvaginal ultrasound?

Management of 27 mm Cervical Length at 24 Weeks

For a pregnant woman at 24 weeks with a cervical length of 27 mm and no history of spontaneous preterm birth, vaginal progesterone should be considered based on shared decision-making, as this measurement falls in the borderline range (21-25 mm threshold for strong recommendation, but 27 mm warrants discussion given individual risk factors). 1

Evidence-Based Management Algorithm

Cervical Length Interpretation at 24 Weeks

• A cervical length of 27 mm at 24 weeks falls just above the 25 mm threshold that defines "short cervix" but below the mean cervical length of approximately 35 mm at this gestational age. 2
• The relative risk of spontaneous preterm delivery increases progressively as cervical length decreases below the 50th percentile (35 mm), with a cervical length at the 25th percentile (30 mm) conferring a 3.79-fold increased risk and measurements at the 10th percentile (26 mm) conferring a 6.19-fold increased risk. 2
• This patient's measurement of 27 mm places her between the 10th and 25th percentiles, indicating elevated but not dramatically high risk. 2

Treatment Recommendations by Cervical Length

For cervical length ≤20 mm: Vaginal progesterone is strongly recommended (GRADE 1A) to reduce preterm birth risk. 1

For cervical length 21-25 mm: Vaginal progesterone should be considered through shared decision-making (GRADE 1B). 1

For cervical length 26-29 mm (this patient): While not explicitly addressed in the strongest guidelines, approximately 15% of women in this range will develop cervical shortening to ≤25 mm before 24 weeks, and those who do have a 16% rate of spontaneous preterm birth <37 weeks. 3

Specific Management Steps

• Initiate discussion about vaginal progesterone (either 90 mg gel or 200 mg micronized capsules daily) given the borderline measurement and documented increased preterm birth risk in this cervical length range. 1

• Schedule follow-up transvaginal ultrasound in 1-2 weeks (before 24 weeks) to assess for progressive cervical shortening, as the mean follow-up interval in similar patients is 1.5 weeks and 15% will shorten to ≤25 mm. 3

• If cervical length decreases to ≤25 mm on follow-up: Strongly recommend vaginal progesterone initiation. 1

• If cervical length decreases to ≤20 mm on follow-up: Initiate vaginal progesterone immediately (GRADE 1A recommendation). 1

Interventions NOT Recommended

• Cervical cerclage is not indicated for this patient, as cerclage has not been shown to reduce preterm birth in women without prior spontaneous preterm birth who have cervical lengths of 10-25 mm (GRADE 1B recommendation against). 1, 4

• 17-alpha hydroxyprogesterone caproate (17-OHPC) should not be prescribed, as it has not demonstrated efficacy for short cervix treatment and FDA approval was withdrawn in 2023 (GRADE 1B recommendation against). 1

• Cervical pessary should not be used due to conflicting trial data, with one large multinational study showing no benefit (RR 1.12,95% CI 0.75-1.69) and recent safety concerns. 1

• Expectant management alone is suboptimal given the documented increased preterm birth risk at this cervical length and the availability of effective intervention (vaginal progesterone). 1, 3

Critical Clinical Considerations

• The decision between options B (vaginal progesterone) and C (expectant management) hinges on shared decision-making, but the evidence favors intervention given that 27 mm is close to the 25 mm threshold and follow-up may reveal further shortening. 1, 3

• Women with initial cervical length 26-29 mm who subsequently develop short cervix (≤25 mm) have significantly higher spontaneous preterm birth rates (16%) compared to low-risk women with cervical length >25 mm (3%). 3

• The mean cervical length in women who develop subsequent short cervix is 26.7 mm versus 27.8 mm in those who don't, placing this patient at meaningful risk. 3

Answer to Multiple Choice Question

The best answer is B (Vaginal progesterone), though close follow-up with repeat ultrasound is also essential. While the strongest GRADE 1A recommendation applies to cervical length ≤20 mm, and GRADE 1B applies to 21-25 mm, this patient's measurement of 27 mm warrants proactive management given the 15% risk of progression to short cervix and documented efficacy of vaginal progesterone in preventing preterm birth. 1, 3