Cervical length & Prediction of preterm labor

Current Opinion in Obstetrics & Gynecology 19, April 2007 p.191~195

부산백병원 산부인과 R2 정은정

Abstract

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

Abstract Aymptomatic women c prior cone biopsy, mull

erian anomalies, multiple D&C. Asymptomatic women once short cervical len

gth prior preterm birth cervical length < 25 mm.

Preventing preterm birth benefit of USG-indicated cerclage(progesterone & indomethacin)

Abstract

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

Abstract

Transvaginal ultrasound cervical length Screening tool for prediction preterm birth Prevention of preterm birth significantly i

mprove health outcomes of pregnant pts & their babies.

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

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 sin

gleton 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

Cervical length as a screening Specific criteria for screening test Cinically important & prevalent condition.

• PTB : main cause of perinatal morbidity & mortality.

Safe & well accepted. 1. safe & no inoculation of bacteria (ex PPROM)

2. well accepted by pregnant women.

3. Pain and severe discomfort < 2%

Cervical length as a screening Recognize disease in asymptomatic phase.

1. Initially, internal os progressively shortens Cx widens along endocervical canal from internal towards external os. external os opens.

2. earliest changes at internal os :asymptomatic, only detected by TVU of Cx.

Well described technique, reliable, reproducible

Cervical length as a screening Have validity

• Digital vs TVU examinations of CL every 2 wks (GA 14 ~GA 30) predict PTBTVU 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 2nd trimester)

Sonographic cervical length :11 mm longer than manual estimations.

TVU superior to manual exam for evaluation of Cx & prediction of preterm birth.

Cervical length as a screening

Intervention prevent outcome. Cervical length shortens, cerclage Other interventions : indomethacin, progest

erone, antibiotics in asymptomatic women & PTL protocol in symptomatic women

Predictive accuracy of CL & prevention of preterm birth in different populations

Low-risk Mean of 35–40 mm (GA 14 ~30 wk ) lower 10th per

centile: 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 ~ 4

4% [sensitivity low] 82% short CL at 24 weeks delivered at or after 35

weeks USG-indicated cerclage not prevent PTB not re

commend cervical length as a routine screening predictor of PTB in low-risk women.

Table 1

Prior preterm birth CL : good predictor of PTB in women at high r

isk(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% ris

k of preterm. Timing of TVU cervical length screening in thi

s population is proposed in Fig. 1.

Timing of TVU cervical length screening prior preterm birth

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

 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 .

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

Multiple gestations CL > 3.5 cm at 18–26 wks : 4% delivered prio

r to 35 wks. Triplet gestations :TVU CL -predictive of PTB More likley short Cx at 24 wks difficult to dis

cern whether short cervix : inherent to women with multi

ple gestations short cervical length later in 2nd trimester in multip

le gestations: <== secondary to rapidly expanding ut putting extra pressure on lower part of Ut (not secondary to insufficient cervix)

Multiple gestations CL < 2.0 cm or > 3.5 cm : prediction of

PTB in twin gestations. CL: prediction of PTB in multiple gestati

ons applicability limited USG-indicated cerclage: recently 21

5% increase in PTB in women c asymptomatic short CL & twin gestations 

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

Post cerclage Similar to other populations, shortening of CL benefit

following cerclage no proven intervention For patients post history-indicated cerclage, if CL follo

wing 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)

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 wors

e predictor of PTB than short cervical length alone

Funneling in normal length Cx (>=25 mm) increases risk for PTB (?) unclear

Other interventions-Indomethacin Most asymptomatic women c short CL: painle

ss 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  

Other interventions- Progesterone Effective in reducing incidence of PTB in wom

en c prior PTB 1/3. Using 17 hydroxy-progesterone caproate in w

omen 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

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  

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

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.

Conclusion Earlier in GA shortening occurs higher risk. Screening frequency: severity of obstetrical H

x, especially in high-risk populations. Prevention strategies,once short cervical leng

th 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

Conclusion Other interventions based on short cervical l

ength indomethacin & progesterone. Recent trial ( use of cervical length & FFN) thr

eatened 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