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Guideline No. 401: Sonographic Cervical Length in Singleton Pregnancies: Techniques and Clinical Applications

      Abstract

      Objectives

      • To assess the association between sonography-derived cervical length measurement and preterm birth.
      • To describe the various techniques to measure cervical length using sonography.
      • To review the natural history of the short cervix.
      • To review the clinical uses, predictive ability, and utility of sonography-measured short cervix.

      Outcomes

      Reduction in rates of prematurity and/or better identification of those at risk, as well as possible prevention of unnecessary interventions.

      Intended Users

      Clinicians involved in the obstetrical management or cervical imaging of patients at increased risk of a short cervix.

      Target Population

      Women at increased risk of a short cervix or at risk of preterm birth.

      Evidence

      Literature published up to June 2019 was retrieved through searches of PubMed and the Cochrane Library using appropriate controlled vocabulary and key words (preterm labour, ultrasound, cervix, cervical insufficiency, transvaginal, transperineal, cervical length, fibronectin). Results were restricted to general and systematic reviews, randomized controlled trials, controlled clinical trials, and observational studies. There were no date or language restrictions. Grey (unpublished) literature was identified through searching the websites of health technology assessment agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies.

      Values

      The evidence and this guideline were reviewed by the Diagnostic Imaging Committee of the Society of Obstetricians and Gynaecologists of Canada, and the recommendations were made and graded according to the rankings of the Canadian Task Force on Preventive Health Care (Online Appendix Table A1).

      Benefits, Harms, Costs

      Preterm birth is a leading cause of perinatal morbidity and mortality. Use of the sonographic technique reviewed in this guideline may help identify women at risk of preterm birth and, in some circumstances, lead to interventions that may reduce the rate of preterm birth.

      SUMMARY STATEMENTS (Canadian Task Force on Preventive Health Care grading in parentheses)

      • 1
        In the general obstetrical population, cervical length is relatively stable over the first 2 trimesters. The natural history of cervical length change may not be useful in identifying women at increased risk of spontaneous preterm birth. Because there may be different patterns, rates, and/or onset of cervical length shortening, repeat assessment of cervical length may be useful in patients at high risk of spontaneous preterm birth (II-2).
      • 2
        Transvaginal sonography can be used to assess the risk of preterm birth in women with a history of spontaneous preterm birth and to differentiate those at higher and lower risk of preterm delivery (II-2).
      • 3
        Cervical length measurement can be used to identify those at increased risk of preterm birth in asymptomatic women at <24 weeks gestation who have other risk factors for preterm birth (uterine anomaly or prior multiple dilatation and evacuation procedures beyond 13 weeks gestation). However, there is insufficient evidence to recommend specific management strategies in this group of women (II-2).
      • 4
        There is no consensus on the optimal timing or frequency of serial evaluations of cervical length. If repeat measurements are performed, they should be done at suitable intervals to minimize the likelihood of observation error (II-2).
      • 5
        No specific randomized trials have evaluated any interventions in asymptomatic women initially diagnosed at or beyond 24 weeks gestation who are at increased risk of preterm birth (e.g., those who have a history of prior spontaneous preterm birth, uterine anomaly, or prior multiple dilatation and evacuation procedures beyond 13 weeks gestation) and who have a short cervical length. However, knowledge of cervicanalal length beyond 24 weeks may help with empiric management strategies for these women, such as relocation and increased surveillance (III).
      • 6
        In women presenting with suspected preterm labour and intact membranes, transvaginal sonographic assessment of cervical length may be used to help stratify the risk of preterm delivery and prevent unnecessary intervention without harm. This information may result in a reduction in late preterm birth, but it is unclear whether it makes a significant clinical difference (II-2B).
      • 7
        Cervical length surveillance is a safe option for patients with a prior sonography indicated cerclage, unclear history of cervical insufficiency, and prior spontaneous preterm birth when compared with routine cerclage based on clinical assessment; it may reduce the need for subsequent cerclage (II-2B).
      • 8
        Transvaginal sonography appears to be safe in preterm prelabour rupture of membranes, but its clinical predictive value is uncertain in this context (II-2).
      • 9
        There is insufficient evidence to support a committee position on the frequency or timing of sonographic cervical length assessment post cerclage. It is unclear if there is significant clinical benefit of such scans (III).
      • 10
        Sonographic cervical length assessment and fetal fibronectin appear to be similar in predictive ability in symptomatic patients, and their combined value may not be significantly different from assessment of cervical length alone. More research is needed in this area (II-2).

      RECOMMENDATIONS (Canadian Task Force on Preventive Health Care grading in parentheses)

      • 1
        Transvaginal sonography is the preferred approach for cervical assessment to identify women at increased risk of spontaneous preterm birth, and it can be offered to women at increased risk of preterm birth (II-2B).
      • 2
        Transperineal sonography can be offered to women at increased risk of preterm birth if transvaginal sonography is either unacceptable or unavailable (II-2B). Transabdominal assessment of cervical length may be a useful alternative for screening under certain conditions.

      Keywords

      Abbreviations:

      LEEP (loop electrosurgical excision procedure), PPROM (preterm premature rupture of membranes)
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      REFERENCES

      1. Institute of Medicine Committee on Understanding Premature Birth, Assuring Healthy Outcomes. The National Academies Collection: Reports funded by National Institutes of Health. In: Behrman RE, Butler AS, editors. Preterm Birth: Causes, Consequences, and Prevention. Washington (DC): National Academies Press: 2007

        • Lawn JE
        • Cousens S
        • Zupan J
        • Lancet Neonatal Survival Steering T
        4 million neonatal deaths: when? Where? Why?.
        Lancet. 2005; 365 (Available from:): 891-900
        • Joseph KS
        • Kramer MS
        • Marcoux S
        • Ohlsson A
        • Wen SW
        • Allen A
        • et al.
        Determinants of preterm birth rates in Canada from 1981 through 1983 and from 1992 through 1994.
        N Engl J Med. 1998; 339 (Available from:): 1434-1439
        • Allen VM
        • Wilson RD
        • Cheung A
        • Genetics Committee, Reproductive Endocrinology and Infertility Committee
        Pregnancy outcomes after assisted reproductive technology.
        J Obstet Gynaecol Can. 2006; 28 (Available from:): 220-233
        • Crowther CA
        • Hiller JE
        • Doyle LW
        Magnesium sulphate for preventing preterm birth in threatened preterm labour.
        Cochrane Database Syst Rev. 2002; (Available from:)CD001060
        • Anotayanonth S
        • Subhedar NV
        • Garner P
        • Neilson JP
        • Harigopal S
        Betamimetics for inhibiting preterm labour.
        Cochrane Database Syst Rev. 2004; (Available from:)CD004352
        • Papatsonis D
        • Flenady V
        • Cole S
        • Liley H
        Oxytocin receptor antagonists for inhibiting preterm labour.
        Cochrane Database Syst Rev. 2005; (Available from:)CD004452
        • Papatsonis DN
        • Van Geijn HP
        • Ader HJ
        • Lange FM
        • Bleker OP
        • Dekker GA
        Nifedipine and ritodrine in the management of preterm labor: a randomized multicenter trial.
        Obstet Gynecol. 1997; 90 (Available from:): 230-234
        • Duckitt K
        • Thornton S
        Nitric oxide donors for the treatment of preterm labour.
        Cochrane Database Syst Rev. 2002; (Available from:)CD002860
        • Smith GN
        • Walker MC
        • Ohlsson A
        • O'Brien K
        • Windrim R
        • Canadian Preterm Labour Nitroglycerin Trial G
        Randomized double-blind placebo-controlled trial of transdermal nitroglycerin for preterm labor.
        Am J Obstet Gynecol. 2007; 196 (Available from:): 37 e1-8
        • Loe SM
        • Sanchez-Ramos L
        • Kaunitz AM
        Assessing the neonatal safety of indomethacin tocolysis: a systematic review with meta-analysis.
        Obstet Gynecol. 2005; 106 (Available from:): 173-179
        • King J
        • Flenady V
        • Cole S
        • Thornton S
        Cyclo-oxygenase (COX) inhibitors for treating preterm labour.
        Cochrane Database Syst Rev. 2005; (Available from:)CD001992
        • King JF
        • Flenady VJ
        • Papatsonis DN
        • Dekker GA
        • Carbonne B
        Calcium channel blockers for inhibiting preterm labour.
        Cochrane Database Syst Rev. 2003; (Available from:)CD002255
        • Lim K
        • Butt K
        • Crane JM
        • et al.
        Ultrasonographic cervical length assessment in predicting preterm birth in singleton pregnancies.
        J Obstet Gynaecol Can. 2011; 33: 486-499
        • Brown R
        • Gagnon R
        • Delisle MF
        No. 373-Cervical Insufficiency and Cervical Cerclage.
        J Obstet Gynaecol Can. 2019; 41 (Available from:): 233-247
        • Butt K
        • Crane J
        • Hutcheon J
        • Lim K
        • Nevo O
        No. 374-Universal Cervical Length Screening.
        J Obstet Gynaecol Can. 2019; 41 (Available from:): 363-74 e1
        • Jain V
        • McDonald SD
        • Mundle WR
        • et al.
        Guideline No. 398: Progesterone for Prevention of Spontaneous Preterm Birth.
        J Obstet Gynaecol Can. 2020; 42: 806-812
        • Lewis D
        • Pelham JJ
        • Done E
        • Sawhney H
        • Talucci M
        • Berghella V
        Uterine contractions in asymptomatic pregnant women with a short cervix on ultrasound.
        J Matern Fetal Neonatal Med. 2005; 18 (Available from:): 325-328
        • Berghella V
        • Iams JD
        • Newman RB
        • Macpherson C
        • Goldenberg RL
        • Mueller-Heubach E
        • et al.
        Frequency of uterine contractions in asymptomatic pregnant women with or without a short cervix on transvaginal ultrasound scan.
        Am J Obstet Gynecol. 2004; 191 (Available from:): 1253-1256
      2. What are the risk factors for preterm labor and birth? Eunice Kennedy Shriver National Institute of Child Health and Human Development, US Deaprtment of health and Human Services. Available from: https://www.nichd.nih.gov/health/topics/preterm/conditioninfo/who_risk.

        • Robinson JN
        • Lockwood CJ
        Preterm birth: Risk factors, interventions for risk reduction, and maternal prognosis.
        UpToDate. 2019; (Available from:)
        • Goldenberg RL
        • Iams JD
        • Mercer BM
        • Meis PJ
        • Moawad A
        • Das A
        • et al.
        The Preterm Prediction Study: toward a multiple-marker test for spontaneous preterm birth.
        Am J Obstet Gynecol. 2001; 185 (Available from:): 643-651
        • Lockwood CJ
        • Kuczynski E
        Markers of risk for preterm delivery.
        J Perinat Med. 1999; 27 (Available from:): 5-20
        • Grimes-Dennis J
        • Berghella V
        Cervical length and prediction of preterm delivery.
        Curr Opin Obstet Gynecol. 2007; 19 (Available from:): 191-195
        • Iams JD
        • Goldenberg RL
        • Meis PJ
        • Mercer BM
        • Moawad A
        • Das A
        • 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 (Available from:): 567-572
        • Tekesin I
        • Eberhart LH
        • Schaefer V
        • Wallwiener D
        • Schmidt S
        Evaluation and validation of a new risk score (CLEOPATRA score) to predict the probability of premature delivery for patients with threatened preterm labor.
        Ultrasound Obstet Gynecol. 2005; 26 (Available from:): 699-706
        • Honest H
        • Bachmann LM
        • Coomarasamy A
        • Gupta JK
        • Kleijnen J
        • Khan KS
        Accuracy of cervical transvaginal sonography in predicting preterm birth: a systematic review.
        Ultrasound Obstet Gynecol. 2003; 22 (Available from:): 305-322
        • Iams JD
        Prediction and early detection of preterm labor.
        Obstet Gynecol. 2003; 101 (Available from:): 402-412
        • Smith V
        • Devane D
        • Begley CM
        • Clarke M
        • Higgins S
        A systematic review and quality assessment of systematic reviews of fetal fibronectin and transvaginal length for predicting preterm birth.
        Eur J Obstet Gynecol Reprod Biol. 2007; 133 (Available from:): 134-142
        • Vendittelli F
        • Volumenie J
        Transvaginal ultrasonography examination of the uterine cervix in hospitalised women undergoing preterm labour.
        Eur J Obstet Gynecol Reprod Biol. 2000; 90 (Available from:): 3-11
        • Goldenberg RL
        • Iams JD
        • Mercer BM
        • Meis PJ
        • Moawad AH
        • Copper RL
        • et al.
        The preterm prediction study: the value of new vs standard risk factors in predicting early and all spontaneous preterm births.
        NICHD MFMU Network. Am J Public Health. 1998; 88 (Available from:): 233-238
        • Honest H
        • Bachmann LM
        • Gupta JK
        • Kleijnen J
        • Khan KS
        Accuracy of cervicovaginal fetal fibronectin test in predicting risk of spontaneous preterm birth: systematic review.
        BMJ. 2002; 325 (Available from:): 301
        • Leitich H
        • Kaider A
        Fetal fibronectin–how useful is it in the prediction of preterm birth?.
        BJOG. 2003; 110 (Available from:): 66-70
        • Skoll A
        • St Louis P
        • Amiri N
        • Delisle MF
        • Lalji S
        The evaluation of the fetal fibronectin test for prediction of preterm delivery in symptomatic patients.
        J Obstet Gynaecol Can. 2006; 28 (Available from:): 206-213
        • FIGO Working Group On Best Practice In Maternal-Fetal M
        • International Federation of G, Obstetrics
        Best practice in maternal-fetal medicine.
        Int J Gynaecol Obstet. 2015; 128 (Available from:): 80-82
        • Romero R
        • Conde-Agudelo A
        • Da Fonseca E
        • O'Brien JM
        • Cetingoz E
        • Creasy GW
        • et al.
        Vaginal progesterone for preventing preterm birth and adverse perinatal outcomes in singleton gestations with a short cervix: a meta-analysis of individual patient data.
        Am J Obstet Gynecol. 2018; 218 (Available from:): 161-180
        • Berghella V
        • Rafael TJ
        • Szychowski JM
        • Rust OA
        • Owen J
        Cerclage for short cervix on ultrasonography in women with singleton gestations and previous preterm birth: a meta-analysis.
        Obstet Gynecol. 2011; 117 (Available from:): 663-671
        • Brown R
        • Gagnon R
        • Delisle MF
        • Materna–Fetal Medicine Committee
        Cervical insufficiency and cervical cerclage.
        J Obstet Gynaecol Can. 2013; 35 (Available from:): 1115-1127
        • Berghella V
        • Ciardulli A
        • Rust OA
        • To M
        • Otsuki K
        • Althuisius S
        • et al.
        Cerclage for sonographic short cervix in singleton gestations without prior spontaneous preterm birth: systematic review and meta-analysis of randomized controlled trials using individual patient-level data.
        Ultrasound Obstet Gynecol. 2017; 50 (Available from:): 569-577
        • Saccone G
        • Maruotti GM
        • Giudicepietro A
        • Martinelli P
        • Italian Preterm Birth Prevention Working G
        Effect of Cervical Pessary on Spontaneous Preterm Birth in Women With Singleton Pregnancies and Short Cervical Length: A Randomized Clinical Trial.
        JAMA. 2017; 318 (Available from:): 2317-2324
      3. The Society for Maternal-Fetal Medicine. CLEAR - Cervical Length Education and Review. 2018. Available from:https://clear.perinatalquality.org.

      4. The Fetal Medicine Foundation. Certificate of Competence in Carvical Assessment. 2018. Available from: https://fetalmedicine.org/fmf-certification/certificates-of-competence/cervical-assessment-1.

      5. The Fetal Medicine Foundation F. Cervical assessment. Available from: https://fetalmedicine.org/fmf-certification/certificates-of-competence/cervical-assessment-1.

        • Guzman ER
        • Pisatowski DM
        • Vintzileos AM
        • Benito CW
        • Hanley ML
        • Ananth CV
        A comparison of ultrasonographically detected cervical changes in response to transfundal pressure, coughing, and standing in predicting cervical incompetence.
        Am J Obstet Gynecol. 1997; 177 (Available from:): 660-665
        • Uquillas KR
        • Fox NS
        • Rebarber A
        • Saltzman DH
        • Klauser CK
        • Roman AS
        A comparison of cervical length measurement techniques for the prediction of spontaneous preterm birth.
        J Matern Fetal Neonatal Med. 2017; 30 (Available from:): 50-53
        • To MS
        • Skentou C
        • Chan C
        • Zagaliki A
        • Nicolaides KH
        Cervical assessment at the routine 23-week scan: standardizing techniques.
        Ultrasound Obstet Gynecol. 2001; 17 (Available from:): 217-219
        • McIntosh J
        • Feltovich H
        • Berghella V
        • Manuck T
        • Society for Maternal-Fetal Medicine
        • Electronic address pso
        The role of routine cervical length screening in selected high- and low-risk women for preterm birth prevention.
        Am J Obstet Gynecol. 2016; 215 (Available from:): B2-B7
        • Committee on Practice Bulletins-Obstetrics TACoO, Gynecologists
        Practice bulletin no. 130: prediction and prevention of preterm birth.
        Obstet Gynecol. 2012; 120 (Available from:): 964-973
        • Newnham JP
        • White SW
        • Meharry S
        • Lee HS
        • Pedretti MK
        • Arrese CA
        • et al.
        Reducing preterm birth by a statewide multifaceted program: an implementation study.
        Am J Obstet Gynecol. 2017; 216 (Available from:): 434-442
        • Saul LL
        • Kurtzman JT
        • Hagemann C
        • Ghamsary M
        • Wing DA
        Is transabdominal sonography of the cervix after voiding a reliable method of cervical length assessment?.
        J Ultrasound Med. 2008; 27 (Available from:): 1305-1311
        • Friedman AM
        • Schwartz N
        • Ludmir J
        • Parry S
        • Bastek JA
        • Sehdev HM
        Can transabdominal ultrasound identify women at high risk for short cervical length?.
        Acta Obstet Gynecol Scand. 2013; 92 (Available from:): 637-641
        • Andersen HF
        • Karimi A
        • Sakala EP
        • Kalugdan R
        Prediction of cervical cerclage outcome by endovaginal ultrasonography.
        Am J Obstet Gynecol. 1994; 171 (Available from:): 1102-1106
        • To MS
        • Skentou C
        • Cicero S
        • Nicolaides KH
        Cervical assessment at the routine 23-weeks' scan: problems with transabdominal sonography.
        Ultrasound Obstet Gynecol. 2000; 15 (Available from:): 292-296
        • Roh HJ
        • Ji YI
        • Jung CH
        • Jeon GH
        • Chun S
        • Cho HJ
        Comparison of cervical lengths using transabdominal and transvaginal sonography in midpregnancy.
        J Ultrasound Med. 2013; 32 (Available from:): 1721-1728
        • Stone PR
        • Chan EH
        • McCowan LM
        • Taylor RS
        • Mitchell JM
        • Consortium S
        Transabdominal scanning of the cervix at the 20-week morphology scan: comparison with transvaginal cervical measurements in a healthy nulliparous population.
        Aust N Z J Obstet Gynaecol. 2010; 50 (Available from:): 523-527
        • Hernandez-Andrade E
        • Romero R
        • Ahn H
        • Hussein Y
        • Yeo L
        • Korzeniewski SJ
        • et al.
        Transabdominal evaluation of uterine cervical length during pregnancy fails to identify a substantial number of women with a short cervix.
        J Matern Fetal Neonatal Med. 2012; 25 (Available from:): 1682-1689
        • Cho HJ
        • Roh HJ
        Correlation Between Cervical Lengths Measured by Transabdominal and Transvaginal Sonography for Predicting Preterm Birth.
        J Ultrasound Med. 2016; 35 (Available from:): 537-544
        • Khalifeh A
        • Berghella V
        Not transabdominal!.
        Am J Obstet Gynecol. 2016; 215 (Available from:): 739-44 e1
        • Stamilio D
        • Carlson LM
        Transabdominal ultrasound is appropriate.
        Am J Obstet Gynecol. 2016; 215 (Available from:): 739-43 e1
        • van Os MA
        • Kleinrouweler CE
        • Schuit E
        • van der Ven AJ
        • Pajkrt E
        • de Groot CJ
        • et al.
        Influence of cut-off value on prevalence of short cervical length.
        Ultrasound Obstet Gynecol. 2017; 49 (Available from:): 330-336
        • 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 Obstet Gynecol. 2001; 17 (Available from:): 335-340
        • O'Hara S
        • Zelesco M
        • Sun Z
        A comparison of ultrasonic measurement techniques for the maternal cervix in the second trimester.
        Australas J Ultrasound Med. 2015; 18 (Available from:): 118-123
        • Raungrongmorakot K
        • Tanmoun N
        • Ruangvutilert P
        • Boriboonhirunsarn D
        • Tontisirin P
        • Butsansee W
        Correlation of uterine cervical length measurement from transabdominal, transperineal and transvaginal ultrasonography.
        J Med Assoc Thai. 2004; 87 (Available from:): 326-332
        • Kurtzman JT
        • Goldsmith LJ
        • Gall SA
        • Spinnato JA
        Transvaginal versus transperineal ultrasonography: a blinded comparison in the assessment of cervical length at midgestation.
        Am J Obstet Gynecol. 1998; 179 (Available from:): 852-857
        • 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 (Available from:): 225-230
        • Carr DB
        • Smith K
        • Parsons L
        • Chansky K
        • Shields LE
        Ultrasonography for cervical length measurement: agreement between transvaginal and translabial techniques.
        Obstet Gynecol. 2000; 96 (Available from:): 554-558
        • Owen J
        • Neely C
        • Northen A
        Transperineal versus endovaginal ultrasonographic examination of the cervix in the midtrimester: a blinded comparison.
        Am J Obstet Gynecol. 1999; 181 (Available from:): 780-783
        • Onderoglu LS
        Digital examination and transperineal ultrasonographic measurement of cervical length to assess risk of preterm delivery.
        Int J Gynaecol Obstet. 1997; 59 (Available from:): 223-228
        • Jackson GM
        • Ludmir J
        • Bader TJ
        The accuracy of digital examination and ultrasound in the evaluation of cervical length.
        Obstet Gynecol. 1992; 79 (Available from:): 214-218
        • Sonek JD
        • Iams JD
        • Blumenfeld M
        • Johnson F
        • Landon M
        • Gabbe S
        Measurement of cervical length in pregnancy: comparison between vaginal ultrasonography and digital examination.
        Obstet Gynecol. 1990; 76 (Available from:): 172-175
        • Berghella V
        • Tolosa JE
        • Kuhlman K
        • Weiner S
        • Bolognese RJ
        • Wapner RJ
        Cervical ultrasonography compared with manual examination as a predictor of preterm delivery.
        Am J Obstet Gynecol. 1997; 177 (Available from:): 723-730
        • Gomez R
        • Galasso M
        • Romero R
        • Mazor M
        • Sorokin Y
        • Goncalves L
        • et al.
        Ultrasonographic examination of the uterine cervix is better than cervical digital examination as a predictor of the likelihood of premature delivery in patients with preterm labor and intact membranes.
        Am J Obstet Gynecol. 1994; 171 (Available from:): 956-964
        • Cook CM
        • Ellwood DA
        A longitudinal study of the cervix in pregnancy using transvaginal ultrasound.
        Br J Obstet Gynaecol. 1996; 103 (Available from:): 16-18
        • Smith CV
        • Anderson JC
        • Matamoros A
        • Rayburn WF
        Transvaginal sonography of cervical width and length during pregnancy.
        J Ultrasound Med. 1992; 11 (Available from:): 465-467
        • Tongsong T
        • Kamprapanth P
        • Pitaksakorn J
        Cervical length in normal pregnancy as measured by transvaginal sonography.
        Int J Gynaecol Obstet. 1997; 58 (Available from:): 313-315
        • 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 (Available from:): 135-139
        • Liabsuetrakul T
        • Suntharasaj T
        • Suwanrath C
        • Leetanaporn R
        • Rattanaprueksachart R
        • Tuntiseranee P
        Serial translabial sonographic measurement of cervical dimensions between 24 and 34 weeks' gestation in pregnant Thai women.
        Ultrasound Obstet Gynecol. 2002; 20 (Available from:): 168-173
        • Heath VC
        • Southall TR
        • Souka AP
        • Elisseou A
        • Nicolaides KH
        Cervical length at 23 weeks of gestation: prediction of spontaneous preterm delivery.
        Ultrasound Obstet Gynecol. 1998; 12 (Available from:): 312-317
        • Dilek TU
        • Yazici G
        • Gurbuz A
        • Tasdelen B
        • Gulhan S
        • Dilek B
        • et al.
        Progressive cervical length changes versus single cervical length measurement by transvaginal ultrasound for prediction of preterm delivery.
        Gynecol Obstet Invest. 2007; 64 (Available from:): 175-179
        • Guzman ER
        • Mellon C
        • Vintzileos AM
        • Ananth CV
        • Walters C
        • Gipson K
        Longitudinal assessment of endocervical canal length between 15 and 24 weeks' gestation in women at risk for pregnancy loss or preterm birth.
        Obstet Gynecol. 1998; 92 (Available from:): 31-37
        • Naim A
        • Haberman S
        • Burgess T
        • Navizedeh N
        • Minkoff H
        Changes in cervical length and the risk of preterm labor.
        Am J Obstet Gynecol. 2002; 186 (Available from:): 887-889
        • Conde-Agudelo A
        • Romero R
        Predictive accuracy of changes intransvaginal sonographic cervical length over time for preterm birth: a systematic review and metaanalysis.
        Am J Obstet Gynecol. 2015; 213 (Available from:): 789-801
        • Yoshizato T
        • Obama H
        • Nojiri T
        • Miyake Y
        • Miyamoto S
        • Kawarabayashi T
        Clinical significance of cervical length shortening before 31 weeks' gestation assessed by longitudinal observation using transvaginal ultrasonography.
        J Obstet Gynaecol Res. 2008; 34 (Available from:): 805-811
        • Esplin MS
        • Elovitz MA
        • Iams JD
        • Parker CB
        • Wapner RJ
        • Grobman WA
        • et al.
        Predictive Accuracy of Serial Transvaginal Cervical Lengths and Quantitative Vaginal Fetal Fibronectin Levels for Spontaneous Preterm Birth Among Nulliparous Women.
        JAMA. 2017; 317 (Available from:): 1047-1056
        • Crane JM
        • Hutchens D
        Use of transvaginal ultrasonography to predict preterm birth in women with a history of preterm birth.
        Ultrasound Obstet Gynecol. 2008; 32 (Available from:): 640-645
        • Berghella V
        • Kuhlman K
        • Weiner S
        • Texeira L
        • Wapner RJ
        Cervical funneling: sonographic criteria predictive of preterm delivery.
        Ultrasound Obstet Gynecol. 1997; 10 (Available from:): 161-166
        • Zilianti M
        • Azuaga A
        • Calderon F
        • Pages G
        • Mendoza G
        Monitoring the effacement of the uterine cervix by transperineal sonography: a new perspective.
        J Ultrasound Med. 1995; 14 (Available from:): 719-724
        • Hertzberg BS
        • Kliewer MA
        • Farrell TA
        • DeLong DM
        Spontaneously changing gravid cervix: clinical implications and prognostic features.
        Radiology. 1995; 196 (Available from:): 721-724
        • To MS
        • Skentou C
        • Liao AW
        • Cacho A
        • Nicolaides KH
        Cervical length and funneling at 23 weeks of gestation in the prediction of spontaneous early preterm delivery.
        Ultrasound Obstet Gynecol. 2001; 18 (Available from:): 200-203
        • Yost NP
        • Owen J
        • Berghella V
        • MacPherson C
        • Swain M
        • Dildy 3rd, GA
        • et al.
        Second-trimester cervical sonography: features other than cervical length to predict spontaneous preterm birth.
        Obstet Gynecol. 2004; 103 (Available from:): 457-462
        • Rust OA
        • Atlas RO
        • Kimmel S
        • Roberts WE
        • Hess LW
        Does the presence of a funnel increase the risk of adverse perinatal outcome in a patient with a short cervix?.
        Am J Obstet Gynecol. 2005; 192 (Available from:): 1060-1066
        • Yang JH
        • Kuhlman K
        • Daly S
        • Berghella V
        Prediction of preterm birth by second trimester cervical sonography in twin pregnancies.
        Ultrasound Obstet Gynecol. 2000; 15 (Available from:): 288-291
        • Berghella V
        • Owen J
        • MacPherson C
        • Yost N
        • Swain M
        • Dildy 3rd, GA
        • et al.
        Natural history of cervical funneling in women at high risk for spontaneous preterm birth.
        Obstet Gynecol. 2007; 109 (Available from:): 863-869
        • Kusanovic JP
        • Espinoza J
        • Romero R
        • Goncalves LF
        • Nien JK
        • Soto E
        • 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 (Available from:): 706-714
        • Adanir I
        • Ozyuncu O
        • Gokmen Karasu AF
        • Onderoglu LS
        Amniotic fluid "sludge"; prevalence and clinical significance of it in asymptomatic patients at high risk for spontaneous preterm delivery.
        J Matern Fetal Neonatal Med. 2018; 31 (Available from:): 135-140
        • Fuchs F
        • Boucoiran I
        • Picard A
        • Dube J
        • Wavrant S
        • Bujold E
        • et al.
        Impact of amniotic fluid "sludge" on the risk of preterm delivery.
        J Matern Fetal Neonatal Med. 2015; 28 (Available from:): 1176-1180
        • Hatanaka AR
        • Mattar R
        • Kawanami TE
        • Franca MS
        • Rolo LC
        • Nomura RM
        • et al.
        Amniotic fluid "sludge" is an independent risk factor for preterm delivery.
        J Matern Fetal Neonatal Med. 2016; 29 (Available from:): 120-125
        • Himaya E
        • Rhalmi N
        • Girard M
        • Tetu A
        • Desgagne J
        • Abdous B
        • et al.
        Midtrimester intra-amniotic sludge and the risk of spontaneous preterm birth.
        Am J Perinatol. 2011; 28 (Available from:): 815-820
        • Saade GR
        • Thom EA
        • Grobman WA
        • Iams JD
        • Mercer BM
        • Reddy UM
        • et al.
        Cervical funneling or intra-amniotic debris and preterm birth among nulliparous women with a midtrimester cervical length less than 30 mm.
        Ultrasound Obstet Gynecol. 2017; (Available from:)
        • Gorski LA
        • Huang WH
        • Iriye BK
        • Hancock J
        Clinical implication of intra-amniotic sludge on ultrasound in patients with cervical cerclage.
        Ultrasound Obstet Gynecol. 2010; 36 (Available from:): 482-485
        • Conde-Agudelo A
        • Romero R
        Vaginal progesterone to prevent preterm birth in pregnant women with a sonographic short cervix: clinical and public health implications.
        Am J Obstet Gynecol. 2016; 214 (Available from:): 235-242
        • Moroz LA
        • Simhan HN
        Rate of sonographic cervical shortening and the risk of spontaneous preterm birth.
        Am J Obstet Gynecol. 2012; 206 (Available from:): 234 e1-5
        • Iams JD
        • Cebrik D
        • Lynch C
        • Behrendt N
        • Das A
        The rate of cervicalchange and the phenotype of spontaneous preterm birth.
        Am J Obstet Gynecol. 2011; 205 (Available from:): 130 e1-6
        • Fox NS
        • Rebarber A
        • Klauser CK
        • Peress D
        • Gutierrez CV
        • Saltzman DH
        Prediction of spontaneous preterm birth in asymptomatic twin pregnancies using the change in cervical length over time.
        Am J ObstetGynecol. 2010; 202 (Available from:): 155 e1-4
        • Crane JM
        • Hutchens D
        Follow-up cervical length in asymptomatic high-risk women and the risk of spontaneous preterm birth.
        J Perinatol. 2011; 31 (Available from:): 318-323
        • Bromley B
        • Shipp TD
        • Benacerraf BR
        Amnion-chorion separation after 17 weeks' gestation.
        Obstet Gynecol. 1999; 94 (Available from:): 1024-1026
        • Hassan SS
        • Romero R
        • Vidyadhari D
        • Fusey S
        • Baxter JK
        • Khandelwal M
        • 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 (Available from:): 18-31
        • Jarde A
        • Lutsiv O
        • Park CK
        • Beyene J
        • Dodd JM
        • Barrett J
        • et al.
        Effectiveness of progesterone, cerclage and pessary for preventing preterm birth in singleton pregnancies: a systematic review and network meta-analysis.
        BJOG. 2017; 124 (Available from:): 1176-1189
        • Andrews WW
        • Copper R
        • Hauth JC
        • Goldenberg RL
        • Neely C
        • Dubard M
        Second-trimester cervical ultrasound: associations with increased risk for recurrent early spontaneous delivery.
        Obstet Gynecol. 2000; 95 (Available from:): 222-226
        • Crane J
        • Scott H
        • Stewart A
        • Chandra S
        • Whittle W
        • Hutchens D
        Transvaginal ultrasonography to predict preterm birth in women with bicornuate or didelphus uterus.
        J Matern Fetal Neonatal Med. 2012; 25 (Available from:): 1960-1964
        • Durnwald CP
        • Walker H
        • Lundy JC
        • Iams JD
        Rates of recurrent preterm birth by obstetrical history and cervical length.
        Am J Obstet Gynecol. 2005; 193 (Available from:): 1170-1174
        • To MS
        • Alfirevic Z
        • Heath VC
        • Cicero S
        • Cacho AM
        • Williamson PR
        • et al.
        Cervical cerclage for prevention of preterm delivery in women with short cervix: randomised controlled trial.
        Lancet. 2004; 363 (Available from:): 1849-1853
        • Szychowski JM
        • Owen J
        • Hankins G
        • Iams J
        • Sheffield J
        • Perez-Delboy A
        • et al.
        Timing of mid-trimester cervical length shortening in high-risk women.
        Ultrasound Obstet Gynecol. 2009; 33 (Available from:): 70-75
        • Airoldi J
        • Berghella V
        • Sehdev H
        • Ludmir J
        Transvaginal ultrasonography of the cervix to predict preterm birth in women with uterine anomalies.
        Obstet Gynecol. 2005; 106 (Available from:): 553-556
        • Crane JM
        • Delaney T
        • Hutchens D
        Transvaginal ultrasonography in the prediction of preterm birth after treatment for cervical intraepithelial neoplasia.
        Obstet Gynecol. 2006; 107 (Available from:): 37-44
        • Berghella V
        • Pereira L
        • Gariepy A
        • Simonazzi G
        Prior cone biopsy: prediction of preterm birth by cervical ultrasound.
        Am J Obstet Gynecol. 2004; 191 (Available from:): 1393-1397
        • Berghella V
        • Daly SF
        • Tolosa JE
        • DiVito MM
        • Chalmers R
        • Garg N
        • et al.
        Prediction of preterm delivery with transvaginal ultrasonography of the cervix in patients with high-risk pregnancies: does cerclage prevent prematurity?.
        Am J Obstet Gynecol. 1999; 181 (Available from:): 809-815
        • Visintine J
        • Berghella V
        • Henning D
        • Baxter J
        Cervical length for prediction of preterm birth in women with multiple prior induced abortions.
        Ultrasound Obstet Gynecol. 2008; 31 (Available from:): 198-200
        • Conner SN
        • Cahill AG
        • Tuuli MG
        • Stamilio DM
        • Odibo AO
        • Roehl KA
        • et al.
        Interval from loop electrosurgical excision procedure to pregnancy and pregnancy outcomes.
        Obstet Gynecol. 2013; 122 (Available from:): 1154-1159
        • Bjorge T
        • Skare GB
        • Bjorge L
        • Trope A
        • Lonnberg S
        Adverse Pregnancy Outcomes After Treatment for Cervical Intraepithelial Neoplasia.
        ObstetGynecol. 2016; 128 (Available from:): 1265-1273
        • Cetingoz E
        • Cam C
        • Sakalli M
        • Karateke A
        • Celik C
        • Sancak A
        Progesterone effects on preterm birth in high-risk pregnancies: a randomized placebo-controlled trial.
        Arch Gynecol Obstet. 2011; 283 (Available from:): 423-429
        • Norman JE
        • Marlow N
        • Messow CM
        • Shennan A
        • Bennett PR
        • Thornton S
        • et al.
        Vaginal progesterone prophylaxis for preterm birth (the OPPTIMUM study): a multicentre, randomised, double-blind trial.
        Lancet. 2016; 387 (Available from:): 2106-2116
        • O'Brien JM
        • Adair CD
        • Lewis DF
        • Hall DR
        • Defranco EA
        • Fusey S
        • et al.
        Progesterone vaginal gel for the reduction of recurrent preterm birth: primary results from a randomized, double-blind, placebo-controlled trial.
        Ultrasound Obstet Gynecol. 2007; 30 (Available from:): 687-696
        • Vintzileos AM
        • Visser GH
        Interventions for women with mid-trimester short cervix: which ones work?.
        Ultrasound Obstet Gynecol. 2017; 49 (Available from:): 295-300
        • Valentin L
        • Bergelin I
        Intra- and interobserver reproducibility of ultrasound measurements of cervical length and width in the second and third trimesters of pregnancy.
        Ultrasound Obstet Gynecol. 2002; 20 (Available from:): 256-262
        • Tsoi E
        • Akmal S
        • Rane S
        • Otigbah C
        • Nicolaides KH
        Ultrasound assessment of cervical length in threatened preterm labor.
        Ultrasound Obstet Gynecol. 2003; 21 (Available from:): 552-555
        • Tsoi E
        • Fuchs IB
        • Rane S
        • Geerts L
        • Nicolaides KH
        Sonographic measurement of cervical length in threatened preterm labor in singleton pregnancies with intact membranes.
        Ultrasound Obstet Gynecol. 2005; 25 (Available from:): 353-356
        • Fuchs IB
        • Henrich W
        • Osthues K
        • Dudenhausen JW
        Sonographic cervical length in singleton pregnancies with intact membranes presenting with threatened preterm labor.
        Ultrasound Obstet Gynecol. 2004; 24 (Available from:): 554-557
        • Daskalakis G
        • Thomakos N
        • Hatziioannou L
        • Mesogitis S
        • Papantoniou N
        • Antsaklis A
        Cervical assessment in women with threatened preterm labor.
        J Matern Fetal Neonatal Med. 2005; 17 (Available from:): 309-312
        • Sotiriadis A
        • Papatheodorou S
        • Kavvadias A
        • Makrydimas G
        Transvaginal cervical length measurement for prediction of preterm birth in women with threatened preterm labor: a meta-analysis.
        Ultrasound Obstet Gynecol. 2010; 35 (Available from:): 54-64
        • Sanin-Blair J
        • Palacio M
        • Delgado J
        • Figueras F
        • Coll O
        • Cabero L
        • et al.
        Impact of ultrasound cervical length assessment on duration of hospital stay in the clinical management of threatened preterm labor.
        Ultrasound Obstet Gynecol. 2004; 24 (Available from:): 756-760
        • Alfirevic Z
        • Allen-Coward H
        • Molina F
        • Vinuesa CP
        • Nicolaides K
        Targeted therapy for threatened preterm labor based on sonographic measurement of the cervical length: a randomized controlled trial.
        Ultrasound Obstet Gynecol. 2007; 29 (Available from:): 47-50
        • Berghella V
        • Palacio M
        • Ness A
        • Alfirevic Z
        • Nicolaides KH
        • Saccone G
        Cervical length screening for prevention of preterm birth in singleton pregnancy with threatened preterm labor: systematic review and meta-analysis of randomized controlled trials using individual patient-level data.
        Ultrasound Obstet Gynecol. 2017; 49 (Available from:): 322-329
        • Suhag A
        • Reina J
        • Sanapo L
        • Martinelli P
        • Saccone G
        • Simonazzi G
        • et al.
        Prior Ultrasound-Indicated Cerclage: Comparison of Cervical Length Screening or History-Indicated Cerclage in the Next Pregnancy.
        Obstet Gynecol. 2015; 126 (Available from:): 962-968
        • Vousden N
        • Hezelgrave N
        • Carter J
        • Seed PT
        • Shennan AH
        Prior ultrasound-indicated cerclage: how should we manage the next pregnancy?.
        Eur J Obstet Gynecol Reprod Biol. 2015; 188 (Available from:): 129-132
        • Kelly S
        • Pollock M
        • Maas B
        • Lefebvre C
        • Manley J
        • Sciscione A
        Early transvaginal ultrasonography versus early cerclage in women with an unclear history of incompetent cervix.
        Am J Obstet Gynecol. 2001; 184 (Available from:): 1097-1099
        • Brown JA
        • Pearson AW
        • Veillon EW
        • Rust OA
        • Chauhan SP
        • Magann EF
        • et al.
        History- or ultrasound-based cerclage placement and adverse perinatal outcomes.
        J Reprod Med. 2011; 56 (Available from:): 385-392
        • Berghella V
        • Mackeen AD
        Cervical length screening with ultrasound-indicated cerclage compared with history-indicated cerclage for prevention of preterm birth: a meta-analysis.
        Obstet Gynecol. 2011; 118 (Available from:): 148-155
        • Alfirevic Z
        • Stampalija T
        • Medley N
        Cervical stitch (cerclage) for preventing preterm birth in singleton pregnancy.
        Cochrane Database Syst Rev. 2017; 6 (Available from:)CD008991
        • Rizzo G
        • Capponi A
        • Angelini E
        • Vlachopoulou A
        • Grassi C
        • Romanini C
        The value of transvaginal ultrasonographic examination of the uterine cervix in predicting preterm delivery in patients with preterm premature rupture of membranes.
        Ultrasound Obstet Gynecol. 1998; 11 (Available from:): 23-29
        • Tsoi E
        • Fuchs I
        • Henrich W
        • Dudenhausen JW
        • Nicolaides KH
        Sonographic measurement of cervical length in preterm prelabor amniorrhexis.
        Ultrasound Obstet Gynecol. 2004; 24 (Available from:): 550-553
        • Fischer RL
        • Austin JD
        Cervical length measurement by translabial sonography in women with preterm premature rupture of membranes: can it be used to predict the latency period or peripartum maternal infection?.
        J Matern Fetal Neonatal Med. 2008; 21 (Available from:): 105-109
        • Carlan SJ
        • Richmond LB
        • O'Brien WF
        Randomized trial of endovaginal ultrasound in preterm premature rupture of membranes.
        Obstet Gynecol. 1997; 89 (Available from:): 458-461
        • Hedriana HL
        • Lanouette JM
        • Haesslein HC
        • McLean LK
        Is there value for serial ultrasonographic assessment of cervical lengths after a cerclage?.
        Am J Obstet Gynecol. 2008; 198 (discussion e6. Available from:): 705 e1-6
        • Dijkstra K
        • Funai EF
        • O'Neill L
        • Rebarber A
        • Paidas MJ
        • Young BK
        Change in cervical length after cerclage as a predictor of preterm delivery.
        Obstet Gynecol. 2000; 96 (Available from:): 346-350
        • Groom KM
        • Shennan AH
        • Bennett PR
        Ultrasound-indicated cervical cerclage: outcome depends on preoperative cervical length and presence of visible membranes at time of cerclage.
        Am J Obstet Gynecol. 2002; 187 (Available from:): 445-449
        • O'Brien JM
        • Hill AL
        • Barton JR
        Funneling to the stitch: an informative ultrasonographic finding after cervical cerclage.
        Ultrasound Obstet Gynecol. 2002; 20 (Available from:): 252-255
        • Knight JC
        • Tenbrink E
        • Sheng J
        • Patil AS
        Anterior uterocervical angle measurement improves prediction of cerclage failure.
        J Perinatol. 2017; 37 (Available from:): 375-379
        • Guzman ER
        • Houlihan C
        • Vintzileos A
        • Ivan J
        • Benito C
        • Kappy K
        The significance of transvaginal ultrasonographic evaluation of the cervix in women treated with emergency cerclage.
        Am J Obstet Gynecol. 1996; 175 (Available from:): 471-476
        • Miller ES
        • Gerber SE
        Association between sonographic cervical appearance and preterm delivery after a history-indicated cerclage.
        J Ultrasound Med. 2014; 33 (Available from:): 2181-2186
        • Fuchs F
        • Bouyer J
        • Fernandez H
        • Gervaise A
        • Frydman R
        • Senat MV
        Ultrasound cervical length measurement for prediction of delivery before 32 weeks in women with emergency cerclage for cervical insufficiency.
        Int J Gynaecol Obstet. 2010; 110 (Available from:): 245-248
        • Drassinower D
        • Vink J
        • Pessel C
        • Vani K
        • Brubaker SG
        • Zork N
        • et al.
        Effect of cervical cerclage on rate of cervical shortening.
        Ultrasound Obstet Gynecol. 2015; 46 (Available from:): 718-723
        • Heath VC
        • Daskalakis G
        • Zagaliki A
        • Carvalho M
        • Nicolaides KH
        Cervicovaginal fibronectin and cervical length at 23 weeks of gestation: relative risk of early preterm delivery.
        BJOG. 2000; 107 (Available from:): 1276-1281
        • Hincz P
        • Wilczynski J
        • Kozarzewski M
        • Szaflik K
        Two-step test: the combined use of fetal fibronectin and sonographic examination of the uterine cervix for prediction of preterm delivery in symptomatic patients.
        Acta Obstet Gynecol Scand. 2002; 81 (Available from:): 58-63
        • Iams JD
        • Goldenberg RL
        • Mercer BM
        • Moawad A
        • Thom E
        • Meis PJ
        • et al.
        The Preterm Prediction Study: recurrence risk of spontaneous preterm birth. National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network.
        Am J Obstet Gynecol. 1998; 178 (Available from:): 1035-1040
        • Iams JD
        • Goldenberg RL
        • Mercer BM
        • Moawad AH
        • Meis PJ
        • Das AF
        • et al.
        The preterm prediction study: can low-risk women destined for spontaneous preterm birth be identified?.
        Am J Obstet Gynecol. 2001; 184 (Available from:): 652-655
        • Tsoi E
        • Akmal S
        • Geerts L
        • Jeffery B
        • Nicolaides KH
        Sonographic measurement of cervical length and fetal fibronectin testing in threatened preterm labor.
        Ultrasound Obstet Gynecol. 2006; 27 (Available from:): 368-372
        • Magro-Malosso E
        • Seravalli V
        • Cozzolino M
        • Spitaleri M
        • Susini T
        • Di Tommaso M
        Prediction of preterm delivery by fetal fibronectin in symptomatic and asymptomatic women with cervical length </=20 mm.
        J Matern Fetal Neonatal Med. 2017; 30 (Available from:): 294-297
        • Zhou MX
        • Zhou J
        • Bao Y
        • Chen YQ
        • Cai C
        Evaluation of the ability of cervical length and fetal fibronectin measurement to predict preterm delivery in asymptomatic women with risk factors.
        J Matern Fetal Neonatal Med. 2015; 28 (Available from:): 153-157
        • Abbott DS
        • Hezelgrave NL
        • Seed PT
        • Norman JE
        • David AL
        • Bennett PR
        • et al.
        Quantitative fetal fibronectin to predict preterm birth in asymptomatic women at high risk.
        Obstet Gynecol. 2015; 125 (Available from:): 1168-1176
        • Bruijn M
        • Vis JY
        • Wilms FF
        • Oudijk MA
        • Kwee A
        • Porath MM
        • et al.
        Quantitative fetal fibronectin testing in combination with cervical length measurement in the prediction of spontaneous preterm delivery in symptomatic women.
        BJOG. 2016; 123 (Available from:): 1965-1971
        • Bruijn MM
        • Kamphuis EI
        • Hoesli IM
        • Martinez de Tejada B
        • Loccufier AR
        • Kuhnert M
        • et al.
        The predictive value of quantitative fibronectin testing in combination with cervical length measurement in symptomatic women.
        Am J Obstet Gynecol. 2016; 215 (Available from:): 793 e1-e8
        • 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 labor and intact membranes.
        Am J Obstet Gynecol. 1996; 175 (Available from:): 1146-1151
        • DeFranco EA
        • Lewis DF
        • Odibo AO
        Improving the screening accuracy for preterm labor: is the combination of fetal fibronectin and cervical length in symptomatic patients a useful predictor of preterm birth? A systematic review.
        Am J Obstet Gynecol. 2013; 208 (Available from:): 233 e1-6
        • Grobman WA
        • Welshman EE
        • Calhoun EA
        Does fetal fibronectin use in the diagnosis of preterm labor affect physician behavior and health care costs? A randomized trial.
        Am J Obstet Gynecol. 2004; 191 (Available from:): 235-240
        • van Baaren GJ
        • Vis JY
        • Wilms FF
        • Oudijk MA
        • Kwee A
        • Porath MM
        • et al.
        Cost-effectiveness of diagnostic testing strategies including cervical-length measurement and fibronectin testing in women with symptoms of preterm labor.
        Ultrasound Obstet Gynecol. 2018; 51 (Available from:): 596-603
        • Berghella V
        • Saccone G
        Fetal fibronectin testing for prevention of preterm birth in singleton pregnancies with threatened preterm labor: a systematic review and metaanalysis of randomized controlled trials.
        Am J Obstet Gynecol. 2016; 215 (Available from:): 431-438
        • Mozurkewich EL
        • Naglie G
        • Krahn MD
        • Hayashi RH
        Predicting preterm birth: a cost-effectiveness analysis.
        Am J Obstet Gynecol. 2000; 182 (Available from:): 1589-1598