Cervical length

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Cervical length Prediction of preterm labor

• Current Opinion in Obstetrics Gynecology 19,
  April 2007 p.191195
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Abstract

• Purpose of review summary in clinical use of
  cervical length for prediction of preterm birth.

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Abstract

• Aymptomatic women c prior cone biopsy, mullerian
  anomalies, multiple DC.
• Asymptomatic women once short cervical length
• prior preterm birth
• cervical length lt 25 mm.
• Preventing preterm birth ? benefit of
  USG-indicated cerclage(progesterone
  indomethacin)

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Abstract

• Symptomatic preterm labor knowledge of cervical
  length (fetal fibronectin) ? beneficial
• Time to triage
• Reduction of preterm birth

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Abstract

• Transvaginal ultrasound cervical length
• Screening tool for prediction preterm birth
• Prevention of preterm birth ? significantly
  improve health outcomes of pregnant pts their
  babies.

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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

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Cervical length by transvaginal ultrasound

• Best predictive accuracy CL lt 25 mm.
• Different populations (Spontaneous PTB ltGA 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

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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 lt 2

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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

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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 (1516 of primipara 1735 of
  multipara 12 cm dilated Cx in late 2nd
  trimester)
• Sonographic cervical length 11 mm longer than
  manual estimations.
• ? TVU superior to manual exam for evaluation of
  Cx prediction of preterm birth.

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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

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Predictive accuracy of CL prevention of preterm
birth in different populations
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Low-risk

• Mean of 3540 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 1534 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.

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Table 1
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Prior preterm birth

• CL good predictor of PTB in women at high
  risk(prior PTB ).
• Sensitivity 6080, positive predictive value
  70 ( CL lt 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.

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Timing of TVU cervical length screening prior
preterm birth
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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 lt35 weeks

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 Other high-risk women

• Women with prior cone biopsy , prior multiple
  DEs 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 .

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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 lt2 cm 100 predictive value for
  PTB ( before 28 wks )
• Cervical length lt2.5 cm (at 24 weeks) strong
  predictor of PTB

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Multiple gestations

• CL gt 3.5 cm at 1826 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 lt secondary to rapidly
  expanding ut putting extra pressure on lower
  part of Ut (not secondary to insufficient cervix)

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Multiple gestations

• CL lt 2.0 cm or gt 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 

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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 lt2.5 cm CL above cerclage of lt 1 cm ? best
  predictors of PTB

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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 lt 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)

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Funneling

• lt25 funneling not associated risk for PTB ?
• gt 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 (gt25 mm) increases
  risk for PTB (?) ? unclear

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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 lt 25 mm on TVU at
  1624 weeks ? Indomethacin
• 31 decrease in PTB before 35 wks
• 86 decrease in PTB before 24 wks  

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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

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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  

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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

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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.

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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 lt 25 mm at 1623 wks with
  singleton gestation

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Conclusion

• Other interventions based on short cervical
  length? indomethacin progesterone.
• Recent trial ( use of cervical length FFN)
  threatened 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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