Clinical Review

How to manage a short cervix to lower the risk of preterm delivery

OBG Manag. 2010 May;22(5):36-50

References

1. Hamilton BE, Martin JA, Ventura SJ. Births: Preliminary data for 2007. National vital statistics reports; 2009;57(12). National Center for Health Statistics Web site. http://www.cdc.gov/nchs/data/nvsr/nvsr57/nvsr57_12.pdf. March 18, 2009. Accessed March 30, 2010.

2. Iams JD, Johnson FF, Sonek J, et al. Cervical competence as a continuum: a study of ultrasonographic cervical length and obstetric performance. Am J Obstet Gynecol. 1995;172(4 pt 1):1097-1106.

3. Iams JD, Goldenberg RL, Meis PJ, et al. The length of the cervix and the risk of spontaneous premature delivery. National Institute of Child Health and Human Development Maternal Fetal Medicine Unit Network. N Engl J Med. 1996;334(9):567-572.

4. Clinical Management Guidelines for Obstetrician-Gynecologists. No. 43, May 2003: Management of Preterm Labor. Obstet Gynecol. 2003;101(5 pt 1):1039-1047.

5. Owen J, Iams JD, Hauth JC. Vaginal sonography and cervical incompetence. Am J Obstet Gynecol. 2003;188(2):586-596.

6. Harger JH. Cerclage and cervical insufficiency: an evidence-based analysis. Obstet Gynecol. 2002;100(6):1313-1327.

7. Clinical Management Guidelines for Obstetrician-Gynecologists. No. 48, Nov 2003: Cervical insufficiency. Obstet Gynecol. 2003;102(5 pt 1):1091-1099.

8. Kusanovic JP, Espinoza J, Romero R, et al. Clinical significance of the presence of amniotic fluid ‘sludge’ in asymptomatic patients at high risk for spontaneous preterm delivery. Ultrasound Obstet Gynecol. 2007;30(5):706-714.

9. ACOG Practice Bulletin No. 80. Premature rupture of membranes. Obstet Gynecol. 2007;109(4):1007-1020.DOI:10.1097/01.AOG.0000263888.69178.1f.

10. 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.

11. Owen J, Hankins G, Iams JD, et al. Multicenter randomized trial of cerclage for preterm birth prevention in high-risk women with shortened mid-trimester cervical length. Am J Obstet Gynecol. 2009;201(4):375.e1-e8.

12. Simcox R, Seed PT, Bennett P, Teoh TG, Poston L, Shennan AH. A randomized control trial of cervical scanning vs history to determine cerclage in women at high risk of preterm birth (CIRCLE trial). Am J Obstet Gynecol. 2009;200(6):623.e1-e6.

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16. Meis PJ, Klebanoff M, Thom E, et al. For National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. Prevention of recurrent preterm birth by 17 alpha-hydroxyprogesterone caproate. N Engl J Med. 2003;348(24):2379-2385.

17. Norman JE, Mackenzie F, Owen P, et al. Progesterone for the prevention of preterm birth in twin pregnancy (STOPPIT): a randomised, double-blind, placebo-controlled study and meta-analysis. Lancet. 2009;373(9680):2034-2040.

18. Rouse DJ, Caritis SN, Peaceman AM, et al. For National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. A trial of 17 alpha-hydroxyprogesterone caproate to prevent prematurity in twins. N Engl J Med. 2007;357(5):454-461.

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21. DeFranco EA, O’Brien JM, Adair CD, et al. Vaginal progesterone is associated with a decrease in risk for early preterm birth and improved neonatal outcome in women with a short cervix: a secondary analysis from a randomized, double-blind, placebo-controlled trial. Ultrasound Obstet Gynecol. 2007;30(5):697-705.

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The value of cervical-length measurement lies in its high negative predictive value for recurrent spontaneous preterm birth.⁴ As a general rule of thumb, routine assessment of cervical length in asymptomatic women who do not have a history of preterm birth is not recommended because of the high rate of false-positive results and the low positive predictive value for preterm delivery. We also lack an evidence-based consensus on how to manage an abnormally short cervix in these women.

CASE RESOLVED

The patient is counseled to watch for signs of preterm labor and to remain sedentary. Her pregnancy progresses without incident until 40 weeks, when she undergoes induction of labor for oligohydramnios and delivers a healthy infant weighing 3,855 g.

When a short cervix is detected at less than 20 weeks

If a woman has a history of spontaneous preterm birth, a short cervix this early in gestation raises the question of cervical insufficiency. No objective criteria have been devised to identify this condition. Nor is there a widely accepted definition. A reasonable description does exist, however:

…a clinical diagnosis characterized by recurrent painless dilation and spontaneous midtrimester birth, generally in the absence of predisposing conditions such as spontaneous membrane rupture, bleeding, and infection, characteristics that shift the presumed underlying cause away from cervical incompetence and support other components of the preterm birth syndrome.⁵

A patient who fits this description may be a candidate for cervical cerclage. Alternatively, it is reasonable to reassess the patient in 3 to 7 days, after restricting physical activity, keeping in mind the pitfalls of TVUS assessment of the lower uterine segment in early gestation (see the box on imaging). If cervical length remains short, consider cerclage.^6,7

Watch for inflammation

Occasionally, echogenic material is observed in the amniotic fluid at the level of a short cervix. This debris is an inflammatory exudate of fibrin, white blood cells, and bacteria. The presence of this sludge (FIGURE 3) signifies a risk of preterm birth much greater than that associated with a short cervix alone.⁸ Because cerclage in the presence of inflammation may further heighten the risk of spontaneous preterm birth, I recommend caution.

FIGURE 3 Watch for signs of inflammation

When inflammatory exudate (asterisk) is identified at the level of a short cervix, the risk of spontaneous preterm birth is elevated beyond the risk associated with a short cervix alone.

When a short cervix is detected between 20 and 24 weeks

CASE 2: Is recurrent preterm birth likely?

A 30-year-old woman 21 weeks pregnant with her second child reports for TVUS. Because her first child was delivered preterm at 30 weeks, she has been undergoing periodic measurement of her cervix. Until today, it has been longer than 25 mm, but now it is 20 mm. What is the best strategy to avert another preterm birth?

If a short cervix (<25 mm) is noted in a high-risk patient at this gestational age, consider the possibility of preterm labor and ruptured membranes. If these conditions are present, they should be managed according to existing guidelines.^4,9 If they are absent, consider cerclage.

A recent meta-analysis of randomized trials of cerclage for the prevention of preterm birth in a singleton, high-risk pregnancy with a short cervix suggests that cerclage is associated with a significantly lower risk of delivery before 35 weeks’ gestation (relative risk [RR], 0.61; 95% confidence interval [CI], 0.40–0.92). Among singleton pregnancies involving both a short cervix and a history of midtrimester loss, cerclage is again associated with a reduced likelihood of delivery before 35 weeks (39% vs 23.4%; number needed to treat [NNT], 8; RR, 0.57; 95% CI, 0.33–0.99).¹⁰ A recent randomized trial of cerclage versus no cerclage in women who had a history of spontaneous preterm birth produced similar findings.¹¹ This trial is described in detail in the box.

Another randomized trial compared the relative merits of ultrasound-indicated cerclage for a cervix shorter than 20 mm to a history-indicated cerclage among women with a prior spontaneous preterm birth between 16 and 34 weeks. Thirty-nine of 123 women randomized to the former group received a cerclage, as did 25 of 125 subjects in the latter group. There were no significant differences in the primary outcome of delivery before 34 weeks or secondary measures of loss before 24 weeks, preterm premature membrane rupture, mean gestational age at delivery, or neonatal outcomes. This study was not designed or powered to evaluate the efficacy of cerclage in preventing recurrent, spontaneous preterm birth. It simply compares two ways of selecting high-risk women for cerclage.¹²