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Ultrasound and Other Findings for Causes of Premature Labor

Incompetent Cervix

Cervical incompetence is suspected if cervical shortening, cervical os dilation, and prolapsing fetal membranes into the cervical canal are found in a pregnant patient in the absence

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In the past, it was believed that the cervix was either competent or incompetent. However, recent studies have shown the cervical changes occur on a continuum.73,74The rate of cervical change may differ according to the underly-ing cause, but the change is often gradual and takes place over weeks. The initial site of change is at the internal cervical os. Iams reported that cervical length in the cur-rent pregnancy can be predicted by the gestational age at delivery of the previous preterm birth.74For women who previously had preterm delivery before 32 weeks, the as-sociation between cervical length and preterm birth holds true in subsequent pregnancies.74This leads to the hope that when cervical sonography detects either or both shortening of the cervix and development of membranes funneling at the internal os, timely intervention can be performed with improved perinatal outcome.

The timing of the initial examination and the frequency of follow-up examinations in patients with possible in-competent cervix have not been established. In patients of uterine contractions. The findings can be made clinically

or by ultrasound examination, but cervical sonography can detect those changes earlier.69–73 Although the etiology of premature delivery is often multifactorial, incompetent cervix is felt to be the primary cause in 16% of premature births.2Risk factors such as diethylstilbestrol exposure in utero, cone biopsy of the cervix, and prior cervical laceration identify some of the patients at risk, but the diagnosis of cer-vical incompetence is often made on the basis of a history of midtrimester pregnancy loss associated with painless dilata-tion of the cervix. Often the patient cannot give an accurate description of the events surrounding a prior pregnancy loss.

It is difficult to determine the initiating cause of preterm de-livery when the patient has already embarked upon the final common pathway of premature labor, premature rupture of membranes, and chorioamnionitis. The identification of pa-tients at risk for incompetent cervix is further made difficult because some patients with an incompetent cervix are nulli-parous with no identifiable risk factors.

Figure 11–7 Changing cervix in a patient with a history of second-trimester pregnancy loss. (A) In the supine exam, the closed cervical length was 2.9 cm with 7 mm of wedging of the internal os. (B) After standing for 15 minutes and being scanned upright, the patient’s

closed cervical length was 1.8 cm. The patient delivered at 33 weeks gestational age. (Reproduced with permission from Wong G, Levine D, Ludmir J. Maternal postural challenge as a functional test for cervi-cal incompetence. J Ultrasound Med 1997;16:169–175.)

A B

Figure 11–8 Incompetent cervix. Transabdominal view of the cervix at 19 weeks gestational age in an otherwise asymptomatic patient. (A) The initial image demonstrates ballooning membranes. Calipers meas-ure the open portion of the cervix. (B) Later in the examination, the

cervix appeared normal. Calipers measure the apparent closed cervical length. We recommend that the initial image taken during routine ob-stetric sonography be the view of the cervix. This will help to identify cases of cervical incompetence that would otherwise escape detection.

A B

with a history of pregnancy loss from an incompetent cervix, repeated loss usually occurs at the same gestational age or at an earlier gestational age. Therefore, in subse-quent pregnancies, it is prudent to get an initial cervical scan to establish the baseline cervical length at a time before the gestational age at which the previous loss oc-curred. We recommend follow-up examinations every 1 to 2 weeks, depending on the findings of examinations and the clinical symptoms.

Conventional vaginal sonography to diagnose incompe-tent cervix will only detect a short cervix if cervical changes have taken place before the examination. Func-tional maneuvers, such as transfundal pressure,75 strain-ing,76or scanning the cervix with the patient standing77,78 can elicit early cervical changes and identify patients at risk for incompetent cervix who otherwise would go undi-agnosed. After a positive response is elicited from trans-fundal pressure, many patients have progressive cervical change 1 to 3 weeks later.79In a study by Wong et al, preg-nant patients at 20 to 24 weeks gestation were examined in a standing position to study the effect of posture on the cervix, which may represent a more physiological repro-duction of daily activity than transfundal pressure.78The standing position had no effect on the normal cervix, but patients with greater than 33% shortening in cervical length measured in the standing position after standing for 15 minutes were likely to deliver prematurely (Fig.

11–7). Patients who have a positive test on functional chal-lenge may benefit from close follow up, reduced physical activity, and possibly cervical cerclage.

Because up to one third of patients with cervical in-competence are nulliparous with no identifiable risk fac-tors, when routine obstetrical sonography is performed during the second trimester, it may be beneficial to obtain the view of the cervix at the beginning of the study rather than at the end (Fig. 11–8). This will be a transabdominal view with the limitations mentioned earlier; however, it can identify an unsuspected short cervix or dilated inter-nal os in those low-risk patients. These early cervical views, obtained just after the patient has attained the

supine position, may identify a short cervix that would no longer be apparent after the patient had been lying supine for 30 or more minutes during a routine obstetric scan.

A dynamic or spontaneously changing cervix has been noted during transvaginal scanning of the cervix (Fig.

11–3). Transient, but striking dilation of the internal cervi-cal os and cervicervi-cal canal occurs in the absence of subjective symptoms and objective signs of uterine contractions.80,81 The etiology and mechanism of the dynamically changing cervix are not known. Because many patients with this finding deliver preterm, most patients with a changing cervix are advised to reduce their physical activities. The shorter the measurement of the cervix, the more likely the patient is to deliver preterm.

The treatment of patients at risk for premature deliv-ery from incompetent cervix is controversial. While cer-vical cerclage is still a frequently performed obstetrical procedure, recent studies do not show significant benefit of prophylactic cerclage.82,83Because cerclage is a surgical procedure that can have iatrogenic complications, the currently suggested management approach for patients with an obstetrical history suspicious for cervical incom-petence is to follow them closely with serial cervical sonography instead of placing a prophylactic cerclage.84–86 It is also unclear at present what treatment is most effec-tive when ultrasound examination detects changes in the cervix.87–93The length of prolongation of pregnancy in pa-tients after cervical change is detected on ultrasound ex-amination is similar between those getting cerclage placement versus those getting bed rest.93 Sonography will continue to be important to monitor for progressive change in the cervix. If premature delivery becomes a dis-tinct probability, the premature neonates would benefit by antenatal steroid treatment and receiving perinatal care at the appropriate clinical facilities. If cerclage place-ment is chosen as treatplace-ment, scans performed after the procedure are useful in assessing the result of the cer-clage placement and in monitoring the cervical length and canal dilatation the portion of cervix above the cerclage (Fig. 11–9, Fig. 11–10).94–98 Shortening of the

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Figure 11–9 Cervical ultrasound is useful for following patients who have cerclage placement. (A) The cervix is funneled to and (B) through the cer-clage. These changes in the cervix proximal to the cerclage may not be recognizable by clinical examination alone. Calipers low closed cervical length.

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proximal cervical length (less than 1 cm) is associated with an increased risk of preterm delivery.98 Additional therapeutic maneuvers, such as bed rest or reduced phys-ical activity, are important if there is either significant funneling above the cerclage or only a short portion of closed cervix remaining.

False-Positive Incompetent Cervix

False-positive findings of incompetent cervix can be caused by uterine contractions, improper probe place-ment, and overdistended bladder.99–101The narrowed lower Figure 11–10 Pitfall in measuring cervical length. The suture used in cervical cerclage can create a shadow and obscure landmarks lo-cated beneath the suture. Note the true cervical length (arrows). The distal caliper was placed incorrectly at the time of the study because shadowing from the cerclage obscured the location of the external os, leading to undermeasurement of the cervical length.

Figure 11–11 Nabothian cyst masquerading as funneling of the in-ternal os. (A) Transabdominal view of the cervix shows an anechoic region suggestive of funneling of the internal os. This region is ec-centric to the cervical canal. (B) Transvaginal scan shows two Nabothian cysts in the anterior cervix. A small amount of funneling of

the internal os is present; however, this is not the region in question on the transabdominal scan. (Reproduced with permission from Wong G, Levine D. Sonographic assessment of the cervix in preg-nancy. Semin Ultrasound CT MR 1998;19:370–380.)

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uterine segment during a uterine contraction can mimic funneling of the cervix (Fig. 11–3A). The artifact can be recognized by the abnormally long cervix if measured from the purported internal os, and by the fact that the functional length is close to the length of a normal cervix.

Often, the thickened myometrium associated with uterine contractions can also be visualized. This condition can be clarified by extending the period of observation until the contraction disappears, usually within 20 minutes. Com-pression of the lower uterine segment to produce an im-pression of funneling can also result from an overdis-tended urinary bladder (Fig. 11–3A). A transvaginal scan of the cervix largely eliminates this artifact. Nabothian cysts (Fig. 11–11) and vaginal cysts located near the internal cer-vical os can create the false impression of a dilated internal os.

Premature Rupture of Membranes

When premature rupture of fetal membranes occurs, ex-pectant management is often pursued to gain time for fur-ther fetal maturation. Digital examination of the cervix is contraindicated because of the risk of infection. Speculum examination is often used to help make the diagnosis of rupture of membranes, but visualization of the cervix is not accurate in determining dilatation or effacement of the cervix. Cervical sonography is helpful in assessing cervical dilation and effacement when there is premature rupture of membranes.102It is also useful in excluding the presence of umbilical cord in the lower uterine segment or near the cervical opening. Transvaginal sonography has not been sociated with increased risk of infection when used to as-sess the cervix after premature rupture of membranes.103,104 However, until more studies are available to substantiate

the safety of the transvaginal approach, we prefer to use transperineal sonography to assess the cervix in such a setting.

Summary

Ultrasonography is an important diagnostic tool in as-sessment of the cervix during pregnancy. Cervical length, cervical dilation, and the status of the internal cervical os are all important prognosticators in prema-ture labor and can be safely and accurately assessed by transvaginal and transperineal sonography. A short cer-vical length (less than 2 cm) and funneling of 40 to 50%

of the length of the cervix places patients at high risk of premature delivery. Transvaginal sonography can also be used to diagnose and manage patients with incompetent cervix. Tests to provoke an incompetent cervix (such as transfundal pressure or scanning with the patient up-right) help detect incompetent cervix even earlier in asymptomatic patients. It is hoped that early identifica-tion of these at-risk patients will lead to more effective treatment, resulting in a decrease in perinatal morbidity and mortality.

References

1. Berkowitz G, Papiernik K. Epidemiology or preterm birth. Epi-demiol Res 1993;15:141–143

2. Roberts WE, Morrison JC, Hamer C, Wiser WL. The incidence of preterm labor and specific risk factors. Obstet Gynecol 1990;76 (Suppl 1):85S–89S

3. Martin JA, Hamilton BE, Ventura SJ, Menacker F, Park MM, Sutton PD. Births: final data for 2001. Natl Vital Stat Rep 2002;51:1–

102

4. Centers for Disease Control and Prevention. Contribution of as-sisted reproductive technology and ovulation-inducing drugs to triplet and higher-order multiple births–United States, 1980–1997. MMWR Morb Mortal Wkly Rep 2000;49:535– 538 5. Effer SB, Moutquin JM, Farine D, et al. Neonatal survival rates in

860 singleton live births at 24 and 25 weeks gestational age: a Canadian multicentre study. BJOG 2002;109:740–745

6. Rogowski J. The economics of preterm deliveries. Prenat Neonat Med 1998;3:16–20

7. Wood NS, Marlow N, Costeloe K, Gibson AT, Wilkinson AR. Neuro-logic and developmental disability after extremely preterm birth.

EPICure Study Group. N Engl J Med 2000;343:378–384

8. Wong G, Levine D. Sonographic assessment of the cervix in preg-nancy. Semin Ultrasound CT MR 1998;19:370–380

9. Kurtzman JT, Goldsmith LJ, Gall SA, Spinnato JA. Transvaginal ver-sus transperineal ultrasonography: a blinded comparison in the assessment of cervical length at midgestation. Am J Obstet Gy-necol 1998;179:852–857

10. Cicero S, Skentou C, Souka A, To MS, Nicolaides KH. Cervical length at 22–24 weeks of gestation: comparison of transvaginal and transperineal-translabial ultrasonography. Ultrasound Ob-stet Gynecol 2001;17:335–340

11. Yazici G, Yildiz A, Tiras MB, Arslan M, Kanik A, Oz U. Comparison of transperineal and transvaginal sonography in predicting preterm delivery. J Clin Ultrasound 2004;32:225–230

12. Laing FC, Ryan T, Hadley K, Jeffrey RB, Wing VW. Plastic wrap for US transducer sterility or sanitization. Radiology 1986;160:

846

13. Hertzberg BS, Kliewer MA, Baumeister LA, McNally PB, Fazekas CK. Optimizing transperineal sonographic imaging of the cervix:

the hip elevation technique. J Ultrasound Med 1994;13:933–936;

quiz 1009–1010

14. Burger M, Weber-Rossler T, Willmann M. Measurement of the pregnant cervix by transvaginal sonography: an interobserver study and new standards to improve the interobserver variability.

Ultrasound Obstet Gynecol 1997;9:188–193

15. Berghella V, Kuhlman K, Weiner S, Texeira L, Wapner RJ. Cervical funneling: sonographic criteria predictive of preterm delivery. Ul-trasound Obstet Gynecol 1997;10:161–166

16. Sonek JD, Iams JD, Blumenfeld M, Johnson F, Landon M, Gabbe S.

Measurement of cervical length in pregnancy: comparison be-tween vaginal ultrasonography and digital examination. Obstet Gynecol 1990;76:172–175

17. Mahony BS, Nyberg DA, Luthy DA, Hirsch JH, Hickok DE, Petty CN.

Translabial ultrasound of the third-trimester uterine cervix: corre-lation with digital examination. J Ultrasound Med 1990;9:717–723 18. Gomez R, Galasso M, Romero R, et al. Ultrasonographic tion of the uterine cervix is better than cervical digital examina-tion as a predictor of the likelihood of premature delivery in pa-tients with preterm labor and intact membranes. Am J Obstet Gynecol 1994;171:956–964

19. Berghella V, Tolosa JE, Kuhlman K, Weiner S, Bolognese RJ, Wap-ner RJ. Cervical ultrasonography compared with manual exami-nation as a predictor of preterm delivery. Am J Obstet Gynecol 1997;177:723–730

20. Goldberg J, Newman RB, Rust PF. Interobserver reliability of digi-tal and endovaginal ultrasonographic cervical length measure-ments. Am J Obstet Gynecol 1997;177:853–858

21. Ayers JW, DeGrood RM, Compton AA, Barclay M, Ansbacher R.

Sonographic evaluation of cervical length in pregnancy: diagnosis and management of preterm cervical effacement in patients at risk for premature delivery. Obstet Gynecol 1988;71(6 Pt 1):939–944 22. Andersen HF. Transvaginal and transabdominal ultrasonography of the uterine cervix during pregnancy. J Clin Ultrasound 1991;

19:77–83

23. Brown JE, Thieme GA, Shah DM, Fleischer AC, Boehm FH. Transab-dominal and transvaginal endosonography: evaluation of the cervix and lower uterine segment in pregnancy. Am J Obstet Gy-necol 1986;155:721–726

24. Smith CV, Anderson JC, Matamoros A, Rayburn WF. Transvaginal sonography of cervical width and length during pregnancy. J Ul-trasound Med 1992;11:465–467

25. 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;334:567–572

26. Zorzoli A, Soliani A, Perra M, Caravelli E, Galimberti A, Nicolini U.

Cervical changes throughout pregnancy as assessed by transvagi-nal sonography. Obstet Gynecol 1994;84:960–964

27. Cook CM, Ellwood DA. A longitudinal study of the cervix in preg-nancy using transvaginal ultrasound. Br J Obstet Gynaecol 1996;

103:16–18

28. Kushnir O, Vigil DA, Izquierdo L, Schiff M, Curet LB. Vaginal ultra-sonographic assessment of cervical length changes during nor-mal pregnancy. Am J Obstet Gynecol 1990;162:991–993 29. Gramellini D, Fieni S, Molina E, Berretta R, Vadora E. Transvaginal

sonographic cervical length changes during normal pregnancy. J Ultrasound Med 2002;21:227–232; quiz 234–225

11 Premature Labor

129

14495OB_C11_pgs.qxd 8/16/07 1:52 PM Page 129

49. Guzman ER, Walters C, O’Reilly-Green C, et al. Use of cervical ul-trasonography in prediction of spontaneous preterm birth in triplet gestations. Am J Obstet Gynecol 2000;183:1108–1113 50. Skentou C, Souka AP, To MS, Liao AW, Nicolaides KH. Prediction of

preterm delivery in twins by cervical assessment at 23 weeks. Ul-trasound Obstet Gynecol 2001;17:7–10

51. Souka AP, Heath V, Flint S, Sevastopoulou I, Nicolaides KH. Cervi-cal length at 23 weeks in twins in predicting spontaneous preterm delivery. Obstet Gynecol 1999;94:450–454

52. Guzman ER, Walters C, Ananth CV, et al. A comparison of sono-graphic cervical parameters in predicting spontaneous preterm birth in high-risk singleton gestations. Ultrasound Obstet Gynecol 2001;18:204–210

53. Benham BN, Balducci J, Atlas RO, Rust OA. Risk factors for preterm delivery in patients demonstrating sonographic evidence of pre-mature dilation of the internal os, prolapse of the membranes in the endocervical canal and shortening of the distal cervical seg-ment by second trimester ultrasound. Aust N Z J Obstet Gynaecol 2002;42:46–50

54. Honest H, Bachmann LM, Coomarasamy A, Gupta JK, Kleijnen J, Khan KS. Accuracy of cervical transvaginal sonography in predict-ing preterm birth: a systematic review. Ultrasound Obstet Gy-necol 2003;22:305–322

55. Yost NP, Owen J, Berghella V, et al. Second-trimester cervical sonography: features other than cervical length to predict spon-taneous preterm birth. Obstet Gynecol 2004;103:457–462 56. Rizzo G, Capponi A, Arduini D, Lorido C, Romanini C. The

value of fetal fibronectin in cervical and vaginal secretions and of ultrasonographic examination of the uterine cervix in predicting premature delivery for patients with preterm la-bor and intact membranes. Am J Obstet Gynecol 1996;175:

1146–1151

57. Rozenberg P, Goffinet F, Malagrida L, et al. Evaluating the risk of preterm delivery: a comparison of fetal fibronectin and transvagi-nal ultrasonographic measurement of cervical length. Am J Ob-stet Gynecol 1997;176(1 Pt 1):196–199

58. Iams JD, Casal D, McGregor JA, et al. Fetal fibronectin improves the accuracy of diagnosis of preterm labor. Am J Obstet Gynecol 1995;173:141–145

59. Iams JD. Prediction and early detection of preterm labor. Obstet Gynecol 2003;101:402–412

60. Vavra N, Eppel W, Sevelda P, et al. Serum prostaglandin F2 alpha (PGFM) and oxytocin levels correlate with sonographic changes in the cervix in patients with preterm labor. Arch Gynecol Obstet 1993;253:33–36

61. Kurkinen-Raty M, Ruokonen A, Vuopala S, et al. Combination of cervical interleukin-6 and -8, phosphorylated insulin-like growth factor-binding protein-1 and transvaginal cervical ultrasonogra-phy in assessment of the risk of preterm birth. BJOG 2001;108:

875–881

62. Bartolucci L, Hill WC, Katz M, Gill PJ, Kitzmiller JL. Ultrason-ography in preterm labor. Am J Obstet Gynecol 1984;149:

52–56

63. Iams JD, Paraskos J, Landon MB, Teteris JN, Johnson FF. Cervi-cal sonography in preterm labor. Obstet Gynecol 1994;84:

40–46

64. Murakawa H, Utumi T, Hasegawa I, Tanaka K, Fuzimori R. Evalua-tion of threatened preterm delivery by transvaginal ultrasono-graphic measurement of cervical length. Obstet Gynecol 1993;82:

829–832

65. Rageth JC, Kernen B, Saurenmann E, Unger C. Premature contrac-tions: possible influence of sonographic measurement of cervical 30. Kushnir O, Izquierdo LA, Smith JF, Blankstein J, Curet LB.

Trans-vaginal sonographic measurement of cervical length: evaluation of twin pregnancies. J Reprod Med 1995;40:380–382

31. Eppel W, Schurz B, Frigo P, et al. Vaginal sonography of the cervix in twin pregnancies [in German]. Geburtshilfe Frauenheilkd 1994;54:20–26

32. Carvalho MH, Bittar RE, Brizot ML, Maganha PP, Borges da Fonseca ES, Zugaib M. Cervical length at 11–14 weeks’ and 22–24 weeks’

gestation evaluated by transvaginal sonography, and gestational age at delivery. Ultrasound Obstet Gynecol 2003;21:135–139

gestation evaluated by transvaginal sonography, and gestational age at delivery. Ultrasound Obstet Gynecol 2003;21:135–139