Contributors: Laura Carlson, MD
Updated: October 2019
Short cervix is an important predictor for preterm birth. Screening for short cervix is warranted as the finding of a short cervix is actionable.1,2
For women with a prior history of preterm birth at < 34 weeks, cervical length surveillance can identify women who would benefit from cerclage placement. Data exist that ultrasound-indicated cerclage placed in these women with CL < 25 mm have reduced risk of delivery < 24 weeks and < 37 weeks.3,4 In study protocols which identified this benefit, transvaginal evaluation of cervical length was performed serially between 16 weeks and 22-24 weeks gestation. The mean time for short cervix identification in high risk women is approximately 21 weeks.5
A woman with a singleton gestation and a prior spontaneous preterm singleton delivery should be offered progesterone supplementation beginning at 16-24 weeks gestation to decrease the risk for recurrent preterm delivery.
For those women without prior history of preterm birth, cerclage has not been shown to be beneficial for the finding of short cervix alone. Initiation of vaginal progesterone reduces the risk of preterm birth by approximately 30 % when a cervical length less than 20 mm is identified.6,7
Use of cervical length screening in twin gestations is not routinely recommended as efficacy of vaginal progesterone has not been proven,1,2 and placement of cerclage for finding of short cervix alone has been shown to paradoxically increase the risk of preterm birth in this population.4 However, its use can be considered to assess for study eligibility (i.e. PROSPECT trial). There are no data supporting cervical length screening in higher order gestations. Cervical length screening in multiple gestations is therefore not currently recommended by SMFM outside of research protocols.2
Proposed CL protocol (16 weeks – 22w6d)
- Singleton gestations with no h/o PTB or h/o PTB 34-37 weeks- TVCL screening x1 at 16w-24w with option for patient to opt out. Will perform with anatomy scan.
- Singleton gestations with h/o PTB < 34 wks 16w-22w6d
- No cerclage: serial TVCL q 2 wks
- If > 30 mm: Continue q 2 wk TVCL
- If 25-29 mm: Weekly TVCL
- If < 25 mm: Consider US-indicated cerclage
- Cerclage in place
- No further TVCL screening per SMFM recommendations unless additional concerns arise making the patient a candidate for pessary placement or BMS therapy administration.
- Twin gestations ( MFM office only)
- TVCL x 1 with anatomy to evaluate for trial enrollment without billing to patient (16w-23w6d)
- Consider a second cervical length to evaluate for trial enrollment without billing to patient (16w-23w6d)
- No cerclage: serial TVCL q 2 wks
- Committee on Practice Bulletins-Obstetrics TACoO, Gynecologists. Practice bulletin no. 130: prediction and prevention of preterm birth. Obstet Gynecol. 2012;120(4):964-973.
- Society for Maternal-Fetal Medicine . Electronic address pso, McIntosh J, Feltovich H, Berghella V, Manuck T. The role of routine cervical length screening in selected high- and low-risk women for preterm birth prevention. Am J Obstet Gynecol. 2016;215(3):B2-7.
- Owen J, Hankins G, Iams JD, et al. Multicenter randomized trial of cerclage for preterm birth prevention in high-risk women with shortened midtrimester cervical length. Am J Obstet Gynecol. 2009;201(4):375 e371-378.
- Berghella V, Odibo AO, To MS, Rust OA, Althuisius SM. Cerclage for short cervix on ultrasonography: meta-analysis of trials using individual patient-level data. Obstet Gynecol. 2005;106(1):181-189.
- Szychowski JM, Owen J, Hankins G, et al. Timing of mid-trimester cervical length shortening in high-risk women. Ultrasound Obstet Gynecol. 2009;33(1):70-75.
- Fonseca EB, Celik E, Parra M, Singh M, Nicolaides KH, Fetal Medicine Foundation Second Trimester Screening G. Progesterone and the risk of preterm birth among women with a short cervix. N Engl J Med. 2007;357(5):462-469.
- Hassan SS, Romero R, Vidyadhari D, et al. Vaginal progesterone reduces the rate of preterm birth in women with a sonographic short cervix: a multicenter, randomized, double-blind, placebo-controlled trial. Ultrasound Obstet Gynecol. 2011;38(1):18-31.