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Cervical length & Prediction of preterm labor 	 Cervical length & Prediction of preterm labor
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Cervical length & Prediction of preterm labor Cervical length & Prediction of preterm labor

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  • 1. Cervical length & Prediction of preterm labor Current Opinion in Obstetrics & Gynecology 19, April 2007 p.191~195 부산백병원 산부인과 R2 정은정
  • 2. Abstract
    • Purpose of review: summary in clinical use of cervical length for prediction of preterm birth .
  • 3. Abstract
    • Aymptomatic women c prior cone biopsy, mullerian anomalies, multiple D&C.
    • Asymptomatic women once short cervical length
      • prior preterm birth
      • cervical length < 25 mm.
    • Preventing preterm birth  benefit of USG-indicated cerclage(progesterone & indomethacin)
  • 4. Abstract
    • Symptomatic preterm labor: knowledge of cervical length (fetal fibronectin)  beneficial
      • Time to triage
      • Reduction of preterm birth
  • 5. Abstract
    • Transvaginal ultrasound cervical length
      • Screening tool for prediction preterm birth
      • Prevention of preterm birth  significantly improve health outcomes of pregnant pts & their babies.
  • 6. Introduction
    • Preterm birth (PTB) : over 12% of births in the USA, over 500000/ yr  incidence is increasing .
    • PTB: main cause of perinatal morbidity and mortality  most important in obstetrics
  • 7. Cervical length by transvaginal ultrasound
    • Best predictive accuracy: CL < 25 mm.
    • Different populations (Spontaneous PTB <GA 35 wks)
      • asymptomatic low-risk or high-risk women with singleton gestations,
      • women with twin,triplet pregnancies
      • symptomatic women with preterm labor or preterm premature rupture of membranes (PPROM).
      • pts with cerclage in place.
    • More relevant studies and recent advances
  • 8. Cervical length as a screening
    • Specific criteria for screening test
    • Cinically important & prevalent condition.
      • PTB : main cause of perinatal morbidity & mortality.
    • Safe & well accepted.
      • safe & no inoculation of bacteria (ex PPROM)
      • well accepted by pregnant women.
      • Pain and severe discomfort < 2%
  • 9. Cervical length as a screening
    • Recognize disease in asymptomatic phase.
      • Initially, internal os progressively shortens  Cx widens along endocervical canal from internal towards external os.  external os opens.
      • earliest changes at internal os :asymptomatic,  only detected by TVU of Cx.
    • Well described technique, reliable, reproducible
  • 10. Cervical length as a screening
    • Have validity
      • Digital vs TVU examinations of CL every 2 wks (GA 14 ~GA 30) predict PTB  TVU much stronger
        • subjective
        • not accurate for evaluating internal os and nonspecific (15 – 16% of primipara 17 – 35% of multipara :1 – 2 cm dilated Cx in late 2 nd trimester)
      • Sonographic cervical length :11 mm longer than manual estimations.
      •  TVU superior to manual exam for evaluation of Cx & prediction of preterm birth.
  • 11. Cervical length as a screening
    • Intervention prevent outcome.
      • Cervical length shortens, cerclage
      • Other interventions : indomethacin, progesterone, antibiotics in asymptomatic women & PTL protocol in symptomatic women
  • 12. Predictive accuracy of CL & prevention of preterm birth in different populations
  • 13. Low-risk
    • Mean of 35 – 40 mm (GA 14 ~30 wk ) lower 10th percentile: 25 mm.
    • Progressive shortening of Cx after 30 wks
    • Shorter cervical length  higher risk for PTB.
    • Positive predictive value for CL: 15–34 mm  6 ~ 44% [sensitivity low]
    • 82% short CL at 24 weeks delivered at or after 35 weeks
    • USG-indicated cerclage not prevent PTB  not recommend cervical length as a routine screening predictor of PTB in low-risk women.
  • 14. Table 1
  • 15. Prior preterm birth
    • CL : good predictor of PTB in women at high risk(prior PTB ).
    • Sensitivity 60–80%, positive predictive value: 70% ( CL < 25 mm,GA14~ 18 wks )
    • High-risk pts c nl CL (GA14~ 18 wks ) : 4% risk of preterm.
    • Timing of TVU cervical length screening in this population is proposed in Fig. 1.
  • 16. Timing of TVU cervical length screening prior preterm birth
  • 17. Prior preterm birth
    • We usually stop cervical length measurements at 28 weeks.
    • High-risk women of short cervical length often present with PPROM
    • USG-indicated cerclage (detection of short cervical length): 39% ↓ in PTB <35 weeks
  • 18.   Other high-risk women
    • Women with prior cone biopsy , prior multiple D&Es mullerian anomalies (Table 1).
    • Uterine anomalies & short cervix : 13-fold ↑ in spontaneous preterm birth( ex unicornuate ut: highest rate of preterm birth)
    • Insufficient data to assess efficacy of cerclage in this population .
  • 19. Multiple gestations
    • PTB: one of most significant contributors to morbidity & mortality in multiple gestations.
    • Shortened cervical length :
      • predictive accuracy varies
      • low sensitivity
      • high positive predictive value for PTB
    • Cervical length <2 cm : 100% predictive value for PTB ( before 28 wks )
    • Cervical length <2.5 cm (at 24 weeks) strong predictor of PTB
  • 20. Multiple gestations
    • CL > 3.5 cm at 18 – 26 wks : 4% delivered prior to 35 wks.
    • Triplet gestations :TVU CL -predictive of PTB
    • More likley short Cx at 24 wks  difficult to discern
      • whether short cervix : inherent to women with multiple gestations
      • short cervical length later in 2nd trimester in multiple gestations: <== secondary to rapidly expanding ut putting extra pressure on lower part of Ut (not secondary to insufficient cervix)
  • 21. Multiple gestations
    • CL < 2.0 cm or > 3.5 cm : prediction of PTB in twin gestations.
    • CL: prediction of PTB in multiple gestations  applicability limited
    • USG-indicated cerclage: recently 215% increase in PTB in women c asymptomatic short CL & twin gestations 
  • 22. Post cerclage
    • Evaluation of CL before & after cerclage placement : Cx in length ↑ following cerclage  term delivery incidence ↑
    • Similar predictive accuracy for PTB as CL
    • CL <2.5 cm & CL above cerclage of < 1 cm  best predictors of PTB
  • 23. Post cerclage
    • Similar to other populations, shortening of CL benefit following cerclage  no proven intervention
    • For patients post history-indicated cerclage, if CL following procedure < 25 mm, placing a re-enforcing cerclage  worse prognosis , should not be done.
    • Not recommend routine repeated CL measurement following ultrasound-indicated or physical exam-indicated cerclages ( no intervention studied to affect outcome)
  • 24. Funneling
    • <25% funneling :not associated risk for PTB ↑
    • > 25% funneling : risk for PTB ↑
    • CL : preferred method to screen Cx for risk of PTB,
    • Funneling & short cervical length : much worse predictor of PTB than short cervical length alone
    • Funneling in normal length Cx (>=25 mm) increases risk for PTB (?)  unclear
  • 25. Other interventions-Indomethacin
    • Most asymptomatic women c short CL: painless Ut contractions
    • Indomethacin : effective at preventing PTB at 48 h, 7 days, less than 37 wks with PTL.
    • Asymptomatic women c short CL < 25 mm on TVU at 16 – 24 weeks  Indomethacin
      • 31% decrease in PTB before 35 wks
      • 86% decrease in PTB before 24 wks  
  • 26. Other interventions- Progesterone
    • Effective in reducing incidence of PTB in women c prior PTB 1/3.
    • Using 17 hydroxy-progesterone caproate in women with short CL on TVU.  possible decrease in PTB (Unpublished data ,Nicolaides & colleagues, 2006, International Society of Ultrasound in Obstetrics and Gynecology (ISUOG))
    • Insufficient data to assess efficacy of this intervention
  • 27. Antibiotics
    • Antibiotics for preventing PTB  not very successful in prolongation of pregnance (except PPROM)
    • Most recently, antibiotics for asymptomatic women c short CL : not efficacious in improving outcomes  
  • 28. Preterm labor
    • Symptomatic women with PTL at high risk for PTB, but most of them deliver at term even without interventions.
    • Compared with women in whom cervical length and fetal fibronectin (FFN) results  similar women with CL and FFN available for management decisions were triaged about half an hour earlier& less incidence of PTB
  • 29. Conclusion
    • Cervical length by TVU best available technique for predicting PTB.
    • Safe, well accepted, reliable, valid in all populations studied.
    • Cervical length of less than 25 mm ( 16 ~ 24 weeks) : most reliable threshold for increased risk of PTB.
    • Shorter cervical length  higher risk of PTB.
  • 30. Conclusion
    • Earlier in GA shortening occurs  higher risk.
    • Screening frequency: severity of obstetrical Hx, especially in high-risk populations.
    • Prevention strategies,once short cervical length is detected  benefit from ultrasound-indicated cerclage.
    • Prior preterm birth or 2nd trimester loss  TVU cervical length < 25 mm at 16 – 23 wks with singleton gestation
  • 31. Conclusion
    • Other interventions based on short cervical length  indomethacin & progesterone.
    • Recent trial ( use of cervical length & FFN) t hreatened PTL : shorter time to triage & decreased incidence of PTB.
    • Cervical length significant role in prediction of PTB  Prevention of this common & severe complication
    • Screening tool : potential to significantly improve health outcomes of pregnant pts & babies
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