Preterm Birth, Short Cervix, and Transvaginal Ultrasound: A New ...

A SUPPLEMENT TO 

October 2009 

CONTENTS 

Introduction 

Emily A. DeFranco, DO 

Preterm Birth: 

Clinical Considerations 


Screening With 

Transvaginal Ultrasound 

for Short Cervix: The 

Solution to Preterm Birth? 

Rachel M. Gutkin, MD 

Lawrence D. Platt, MD 

Disclosures 

Emily A. DeFranco, DO, 

has no financial arrangements 

or affiliations with 

commercial or equipment 

companies during the past 

3 years. 

Rachel M. Gutkin, MD, 

has no financial arrangements 

or affiliations with 

commercial or equipment 

companies during the past 

3 years. 

Lawrence D. Platt, MD, 

is a consultant to and 

receives research support 

from GE Medical Systems 

and Philips Medical Systems 

and is an invited 

speaker for Columbia 

Laboratories, Inc. 

Preterm Birth, Short Cervix, 

and Transvaginal Ultrasound: 

A New Urgency 

Preterm birth (PTB) is 

a critical public health 

burden. With a continuous 

rise in the prevalence of 

the condition and increasing 

survival rates for extremely 

preterm and low birthweight 

neonates, PTB has become one 

of the most vexing complex diseases 

encountered in contemporary 

medicine. The current 

rate of PTB (defined as delivery 

prior to 37 weeks of gestation) 

is 12.8%, the highest reported 

rate ever in the United States. 

This represents a 21% increase 

since 1990. 1 

Emily A. DeFranco, DO, is Assistant 

Professor, Maternal-Fetal Medicine, 

Department of Obstetrics and Gynecology, 

University of Cincinnati College of 

Medicine, OH. 

Introduction 


The current rate 

of PTB (defined as 

delivery prior to 37 weeks 

of gestation) is 12.8%, 

the highest reported rate 

ever in the United States. 

This represents a 21% 

increase since 1990. 

Despite its prevalence, PTB 

remains a relatively underappreciated 

condition compared with 

other serious and life-threatening 

disorders. The 2 leading 

causes of death in the United 

States, heart disease and cancer, 

each take the lives of more 

than 500,000 individuals annu- 

Supported by an educational grant from Columbia Laboratories, Inc.

Introduction 

ally. 2 Approximately 1 million 

myocardial infarctions and 1.4 

million new cases of cancer 

occur each year. 3,4 Comparatively, 

PTB is also a highly 

prevalent condition. More 

than 500,000 babies are born 

prematurely every year. 5 The 

economic burden related to 

PTB has been estimated at 

more than $26 billion annually, 

which is a reflection of 

the high cost associated with 

providing care to child and 

adult survivors of this potentially devastating disease. 

6 Depending on the degree of prematurity 

and breadth of complications encountered in the 

neonatal period, survivors are at risk of requiring 

lifelong medical assistance. Without question, 

the financial and emotional ramifications of PTB 

to an unsuspecting family are immeasurable. 

In an effort to address the “seemingly intractable 

problem of preterm birth,” and in response 

to the 2006 Prematurity Research Expansion and 

Education for Mothers who deliver Infants Early 

(PREEMIE) Act (PL 109-450), the Office of the 

Surgeon General convened a multidisciplinary 

conference to focus on awareness, research, and 

future directions to mitigate the disease. 7 The 

recommendations from this conference specifically 

addressed the importance of making the 

prevention of preterm delivery a coordinated 

national health priority. Experts participating in 

the conference specifically outlined the need to 

identify improved biomarkers to predict PTB and 

broaden our understanding of the mechanisms of 

prophylactic progestins, a promising intervention 

for the prevention of prematurity. 

Employing cervical length screening as a 

method of identifying a larger number of women 

who may benefit from PTB intervention could 

yield a significant impact on the overall reduction 

Employing cervical 

length screening as a 

method of identifying a 

larger number of women 

who may benefit from 

PTB intervention could 

yield a significant impact 

on the overall reduction 

in the rate of PTB. 

in the rate of PTB. As universal 

cervical length screening 

is not a routinely employed 

test, the estimate of its effect 

is difficult to ascertain. The 

cost-effectiveness of using 

this screening tool is currently 

unknown. But if routine 

screening of cervical length 

has the potential to identify a 

large number of women destined 

to deliver early, with a 

cost lower than that incurred 

by the potentially preventable 

cases of PTB, a change in our current practice 

of prenatal care may be in our near future. 

Whether to incorporate routine cervical length 

screening by transvaginal ultrasonography in 

the midtrimester of pregnancy into the routine 

prenatal care of all women is a dilemma frequently 

debated. This question is soon likely to 

be answered as new studies further evaluating 

both the efficacy of treatment interventions for a 

short cervix and the cost-effectiveness of cervical 

length screening become available. 

References 

1. Hamilton BE, Martin JA, Ventura SJ. Births: preliminary data 

for 2005. Natl Vital Stat Rep. 2006;55(11):1-18. 

2. Heron M. Deaths: leading causes for 2004. Natl Vital Stat Rep. 

2007;56(5):1-95. 

3. American Heart Association. Heart attack and angina statistics 

(2005). Available at: www.americanheart.org/presenter.jhtml? 

identifier=4591. Accessed September 3, 2009. 

4. American Cancer Society, Surveillance and Health Policy 

Research. Estimated New Cancer Cases and Deaths by Sex, US, 

2009. Available at: www.cancer.org/downloads/stt/CFF2009_ 

EstCD_3.pdf. Accessed September 3, 2009. 

5. March of Dimes. PeriStats. March of Dimes Perinatal Data 

Center. Available at: www.marchofdimes.com/peristats. 

Accessed September 3, 2009. 

6. Behrman R, Butler A. Preterm birth: causes, consequences, and 

prevention. Institute of Medicine (US) Committee on Understanding 

Premature Birth and Assuring Healthy Outcomes. 

Washington, DC: National Academies Press; 2007. 

7. Ashton DM, Lawrence HC 3rd, Adams NL 3rd, Fleischman AR. 

Surgeon General’s Conference on the Prevention of Preterm 

Birth. Obstet Gynecol. 2009;113(4):925-930. 

The Female Patient Supplement OCTOBER 2009

Preterm Birth: Clinical Considerations 


Preterm birth (PTB) is a 

complex disorder with 

multifactorial etiologies 

that remains poorly understood. 

Because of the complexity 

of the condition, the 

identification of an effective 

intervention to prevent PTB 

remains elusive. The pathophysiologic 

mechanisms leading 

to PTB may differ from 

those that occur at term, and 

it is known that if one or more 

risk factors for PTB exist, the likelihood of PTB 

increases. Numerous risk factor scoring systems 

have been proposed for the prediction of 

PTB. Unfortunately, these scoring systems have 

not been proved to reliably predict spontaneous 

PTB, and most lack clinically important reference 

standards. 1 

Risk Factors 

The known risk factors for PTB have differing 

relative risks and vary based upon the 

population in which the risk factors have been 

assessed. Nonetheless, the identification of 

risk factors for PTB can in some instances 

allow treatments to be provided that may be 

helpful to reduce the risk, such as with bacterial 

vaginosis in women with a prior PTB. 

Also, identification of some risk factors such 

as prior PTB may lead to increased surveillance 

by screening for other risks, such as 

infections or shortened cervical length (the 

best predictor of PTB among all risk factors). 

For these reasons, risk factor identification 

remains an important part of routine prenatal 

care for all pregnancies. 

Emily A. DeFranco, DO, is Assistant Professor, Maternal- 

Fetal Medicine, Department of Obstetrics and Gynecology, 

University of Cincinnati College of Medicine, OH. 

A short cervical 

length, measured by 

transvaginal ultrasound 

in the midtrimester of 

pregnancy, has proved 

to be the most useful 

predictor of PTB in all 

populations studied so far. 

Prior history of PTB: Previous 

PTB has long been 

regarded as one of the leading 

risk factors for PTB. The 

rate of recurrence of PTB has 

been estimated to range from 

15% with a single prior PTB 

to more than 30% with 2 

prior PTBs. 2-4 Other studies 

have demonstrated a recurrence 

rate higher than 50%. 5 

The risk of recurrent PTB 

increases with an increasing 

number of prior PTBs as well as very early gestational 

age of prior birth. 2,5-8 

Short cervical length: A short cervical length, 

measured by transvaginal ultrasound in the 

midtrimester of pregnancy, has proved to be the 

most useful predictor of PTB in all populations 

studied so far. These populations include both 

singleton and twin gestations, women with a prior 

PTB, asymptomatic low-risk women, asymptomatic 

high-risk women, and women presenting with 

symptoms of preterm labor, among others. 9 The 

risk of PTB, and thus the positive predictive value 

of shortened cervix, increases as the cervical length 

measurement decreases. Likewise, the same is true 

when shortened cervix is identified at earlier gestational 

ages. 10-12 Some studies have indicated that 

the combination of obstetric history with cervical 

length has a greater than 80% sensitivity to predict 

PTB with a 10% false-positive rate. 13 

Even when screening a low-risk population 

with an overall low prevalence of shortened cervix, 

it has been reported that the risk of an early 

PTB with a significantly shortened cervix (


less of historical factors, may be a useful tool 

to identify women at the highest risk for PTB. 

In turn, identifying the highest risk population 

may enable the implementation of focused interventions 

for those most likely to demonstrate 

a benefit, avoid treatment side effects in those 

least likely to experience PTB, and ultimately 

identify an optimal population on which to 

focus future studies. 

Other known risk factors for 

PTB include the following, as 

well as others 2,15,16 : 

Race: Black race increases the 

risk of PTB, especially with a 

history of prior PTB. 6 

Age: Extremes of maternal 

age, ie, younger than 18 and 

older than 40, increase risk. 

Infection and inflammation: 

The link between infection/ 

inflammation and PTB has 

been accepted for many years. 

Newer evidence demonstrates that when vaginal 

infections (sexually transmitted and other) are 

treated, the rate of PTB is decreased. 2,17,18 

Placental implantation abnormalities: Abnormalities 

such as placenta previa are also known 

to increase the likelihood of PTB, as is vaginal 

bleeding, which commonly occurs with placental 

abnormalities. 

Genetics: Many risk factors for PTB implicate 

an underlying genetic basis for abnormalities of 

birth timing. Studies have demonstrated PTB 

clustering in twins, nontwin siblings, and children 

of those affected by PTB. Likewise, studies 

revealing a close association in the recurrence of 

birth timing among women giving birth to more 

than one infant support a genetic contribution to 

PTB. More recently, specific genes and potential 

patterns of inheritance associated with PTB have 

been suggested. 2,19,20 

Environmental factors: Exposure to tobacco 

and illicit drugs has been linked to PTB. So have 

other factors related to the social and behavioral 

environment, such as lack of prenatal care, short 

Some studies have 

indicated that the 

combination of obstetric 

history with cervical 

length has a greater 

than 80% sensitivity to 

predict PTB with a 10% 

false-positive rate. 

intervals between pregnancies, and low socioeconomic 

status. 5,21,22 

Infertility treatment: The increasing utilization 

of infertility treatments has contributed to a 

rise in PTB, both due to an association between 

infertility and PTB and to the increase in the 

frequency of multifetal gestations resulting from 

ovarian hyperstimulation. 23 

The PTB Patient History 

and Examination 

A routine part of prenatal care 

should be early consideration 

of preexisting risk factors for 

adverse pregnancy outcomes. 

Subsequent integration of 

screening tests and treatments 

as necessary is commonplace 

in obstetric care to 

optimize perinatal outcomes. 

Examples of beneficial prenatal 

screening and treatment 

routines in pregnancy include first-trimester testing 

for sexually transmitted infections, bacteriuria, 

anemia, and many other conditions. Similarly, 

ultrasound screening in pregnancy for aneuploidy 

and congenital malformations is widely accepted as 

routine obstetric care, despite the fact that many 

identified abnormalities are not treatable during 

the antepartum period. 

With a growing understanding of the relative 

importance of preexisting historical risk 

factors for PTB, such as a previous PTB, it has 

become part of routine prenatal screening to 

query whether such a history exists. Now, with a 

breadth of data supporting the predictive value of 

cervical length measures for PTB, some have suggested 

that routine screening of cervical length 

be considered as a method to assess PTB risk. As 

the cost-effectiveness of this approach remains 

uncertain, others have suggested an approach 

incorporating maternal history (ie, prior PTB or 

uterine anomalies) and cervical length assessment 

as a way to optimize the predictive value when 

choosing a PTB screening approach. 12,13 


DeFranco 

Cervical Surveillance 

The optimal gestational ages for screening and 

follow-up intervals for patients chosen for cervical 

length screening have not been well defined. For 

a low-risk patient in which screening with a single 

measure of cervical length may be desirable, a 

reasonable approach would be to assess the cervix 

at the time of the midtrimester comprehensive 

fetal anatomic survey (18 to 22 weeks) and then to 

schedule follow-up if the cervical 

length is abnormally short, 

ie, less than 25 mm. Some may 

suggest an approach of routine 

transabdominal assessment of 

the lower uterine segment followed 

by targeted transvaginal 

cervical length assessment only 

if the cervix appears subjectively short or evidence 

of funneling exists. 24 The disadvantage of this 

approach is the potential for false-negatives with 

the transabdominal approach, since some studies 

have demonstrated a weak correlation of transabdominal 

and transvaginal measures of cervical 

length. 25 The optimal approach for cervical surveillance 

in this population remains uncertain. 

In women with a significant historical risk factor 

for PTB, such as a prior PTB or uterine anomaly, 

planned cervical surveillance with transvaginal 

ultrasound measurement in the midtrimester 

may more selectively identify those at the highest 

risk and subsequently those most likely to benefit 

from therapeutic interventions. 12,13,24 In this 

population, planned cervical length assessments 

could be initiated early in the second trimester, 

at approximately 16 weeks, with routine followup 

thereafter. 24 If the cervix becomes abnormally 

short, weekly follow-up cervical length assessments 

may be prudent. If the patient remains 

asymptomatic and the initial cervical length is 

normal, a follow-up interval of every 2 weeks 

until 24 to 28 weeks could be considered. 

Fetal Fibronectin Screening 

The presence of fetal fibronectin in the cervicovaginal 

fluids has been shown to be one of the 

If the cervix becomes 

abnormally short, weekly 

follow-up cervical length 

assessments may be prudent. 

best predictors of PTB in many populations, 

including both low- and high-risk asymptomatic 

women, those with preterm labor, and twins. 26,27 

Knowledge of the results of fetal fibronectin testing 

has also been associated with a reduced rate 

of PTB before 37 weeks, further demonstrating 

its utility not only as a screening tool but also a 

method of evaluation of women most likely to 

benefit from an intervention. 28 

The positive predictive value 

(PPV) of fetal fibronectin for 

PTB varies widely based on 

the population studied, gestational 

ages, and whether a 

single screen versus sequential 

screening is employed. Overall, 

the PPV of fetal fibronectin 

ranges from 9% to 46%. 27 Some studies have 

applied a strategy of fetal fibronectin and cervical 

length as a combined screening approach to 

maximize the PPV for PTB, but due to variations 

of patient populations studied (asymptomatic vs 

with symptoms of preterm labor), cutoff values 

considered for an abnormal screen, gestational 

ages at screening, and differing outcome measures, 

the true utility of combining the 2 tools 

to improve the prediction of PTB is still incompletely 

understood. 

References 

1. Honest H, Bachmann LM, Sundaram R, Gupta JK, Kleijnen J, 

Khan KS. The accuracy of risk scores in predicting PTB: a 

systematic review. J Obstet Gynaecol. 2004;24(4):343-359. 

2. ACOG. ACOG practice bulletin: Cervical insufficiency. Obstet 

Gynecol. 2003;102(5 Pt 1):1091-1099. 

3. Petrini JR, Callaghan WM, Klebanoff M, et al. Estimated 

effect of 17 alpha-hydroxyprogesterone caproate on preterm 

birth in the United States. Obstet Gynecol. 2005;105(2):267-672. 

4. Carr-Hill RA, Hall MH. The repetition of spontaneous preterm 

labour. Br J Obstetrics Gynaecol. 1985;92(9):921-928. 

5. Meis PJ, Klebanoff M, Thom E, et al. Prevention of recurrent 

preterm delivery by 17 alpha-hydroxyprogesterone caproate. 

N Engl J Med. 2003;348(24):2379-2385. 

6. Kistka ZA, Palomar L, Lee KA, et al. Racial disparity in the 

frequency of recurrence of preterm birth. Am J Obstet Gynecol. 

2007;196(2):131.e1-e6. 

7. da Fonseca EB, Bittar RE, Carvalho MH, Zugaib M. Prophylactic 

administration of progesterone by vaginal suppository to 

reduce the incidence of spontaneous preterm birth in women at 

increased risk: a randomized placebo-controlled double-blind 

study. Am J Obstet Gynecol. 2003;188(2):419-424. 

The The Female Patient SUPPLEMENT Supplement November OCTOBER 2007 2009


8. O’Brien JM, Adair CD, Lewis DF, 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(5):687-696. 

9. Berghella V, Baxter JK, Hendrix NW. Cervical assessment by 

ultrasound for preventing preterm delivery. Cochrane Database 

Syst Rev. 2009;(3):CD007235. 

10. Berghella V, Roman A, Daskalakis C, Ness A, Baxter JK. Gestational 

age at cervical length measurement and incidence of 

preterm birth. Obstet Gynecol. 2007;110(2 Pt 1):311-317. 

11. Grimes-Dennis J, Berghella V. Cervical length and prediction of 

preterm delivery. Curr Opin Obstet Gynecol. 2007;19(2):191-195. 

12. Crane JM, Hutchens D. Transvaginal sonographic measurement 

of cervical length to predict preterm birth in asymptomatic 

women at increased risk: a systematic review. Ultrasound 

Obstet Gynecol. 2008;31(5):579-587. 

13. Celik E, To M, Gajewska K, Smith GC, Nicolaides KH. 

Cervical length and obstetric history predict spontaneous 

preterm birth: development and validation of a model to provide 

individualized risk assessment. Ultrasound Obstet Gynecol. 

2008;31(5):549-554. 

14. Fonseca EB, Celik E, Parra M, Singh M, Nicolaides KH. Progesterone 

and the risk of preterm birth among women with a 

short cervix. N Engl J Med. 2007;357(5):462-469. 

15. Pschirrer ER, Monga M. Risk factors for preterm labor. Clin 


16. Robinson JN, Regan JA, Norwitz ER. The epidemiology of 

preterm labor. Semin Perinatol. 2001;25(4):204-214. 

17. Swadpanich U, Lumbiganon P, Prasertcharoensook W, Laopaiboon 

M. Antenatal lower genital tract infection screening and 

treatment programs for preventing preterm delivery. Cochrane 

Database Syst Rev. 2008;(2):CD006178. 

18. Thinkhamrop J, Hofmeyr GJ, Adetoro O, Lumbiganon P. 

Prophylactic antibiotic administration in pregnancy to prevent 

infectious morbidity and mortality. Cochrane Database Syst Rev. 

2002;(4):CD002250. 

19. Chaudhari BP, Plunkett J, Ratajczak CK, Shen TT, 

DeFranco EA, Muglia LJ. The genetics of birth timing: 

insights into a fundamental component of human development. 

Clin Genet. 2008;74(6):493-501. 

20. Plunkett J, Feitosa MF, Trusgnich M, et al. Mother’s genome 

or maternally-inherited genes acting in the fetus influence 

gestational age in familial preterm birth. Hum Hered. 

2009;68(3):209-219. 

21. DeFranco EA, Lian M, Muglia LA, Schootman M. Area-level 

poverty and preterm birth risk: a population-based multilevel 

analysis. BMC Public Health. 2008;8:316. 

22. DeFranco EA, Stamilio DM, Boslaugh SE, Gross GA, Muglia LJ. 

A short interpregnancy interval is a risk factor for preterm 

birth and its recurrence. Am J Obstet Gynecol. 2007;197(3): 

264.e1-e6. 

23. Reddy UM, Wapner RJ, Rebar RW, Tasca RJ. Infertility, 

assisted reproductive technology, and adverse pregnancy outcomes: 

executive summary of a National Institute of Child 

Health and Human Development workshop. Obstet Gynecol. 

2007;109(4):967-977. 

24. ACOG. ACOG Practice Bulletin No 101: Ultrasonography in 

pregnancy. Obstet Gynecol. 2009;113(2 Pt 1):451-461. 

25. 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(4): 

292-296. 

26. Ashton DM, Lawrence HC 3rd, Adams NL 3rd, Fleischman AR. 

Surgeon General’s Conference on the Prevention of Preterm 

Birth. Obstet Gynecol. 2009;113(4):925-930. 

27. Leitich H, Egarter C, Kaider A, Hohlagschwandtner M, 

Berghammer P, Husslein P. Cervicovaginal fetal fibronectin 

as a marker for preterm delivery: a meta-analysis. Am J Obstet 

Gynecol. 1999;180(5):1169-1176. 

28. Berghella V, Hayes E, Visintine J, Baxter JK. Fetal fibronectin 

testing for reducing the risk of preterm birth. Cochrane Database 

Syst Rev. 2008;(4):CD006843. 


Screening With Transvaginal Ultrasound for 

Short Cervix: The Solution to Preterm Birth? 

Rachel M. Gutkin, MD; Lawrence D. Platt, MD 

Screening for short cervix 

with transvaginal 

ultrasound (TVU) is a 

challenging conundrum: The 

technique has been shown 

to accurately predict preterm 

birth (PTB), but the options 

for utilization are still unclear. 

Who should be screened, and what action, if 

any, should be taken based on the results? 

It is well established that the relative risk of 

PTB increases with decreasing cervical length 

combined with increasing gestational age. 1,2 

It is also well established that a short cervix is 

present in all preterm births. 3 It makes sense, 

then, that predicting which women have a 

risk of short cervix and identifying gravid 

women who have short cervix will improve 

the ability to prevent PTB. While TVU is 

a screening test, not a diagnostic test, it is a 

perfect tool with which to accomplish these 

important goals. 

The accuracy of TVU over transabdominal 

ultrasound has been established. 4 It has been 

clearly proved to be reproducible when proper 

technique is applied. 3 The body of evidence supporting 

the use of TVU for identifying the short 

cervix is abundant. TVU has been established as 

very safe, without statistically significant bacterial 

inoculation effect. 5 It has also been used in 

the scenario of preterm premature rupture of 

membranes. 6 However, in these cases it should be 

used with caution. The use of TVU has been well 

received by patients. 7 

Who should be 

screened, and what action, 

if any, should be taken 

based on the results? 

It is surprising, therefore, 

that the routine use of TVU 

is more limited than would 

be expected. As an effective, 

reproducible technique, TVU, 

if put to optimal use in clinical 

practice, has the potential to 

identify a pregnancy at risk for 

PTB much earlier. Once identified, the potential 

to take preventive action exists. Whether that 

action is to simply put the patient on bed rest, 

place a cerclage, insert a pessary, or treat with 

progesterone remains in question. 8,9 This article 

will briefly explore the current clinical guidelines, 

data on TVU screening, and issues with clinical 

management, as well as provide an overview of 

TVU screening technique (Sidebar on pages 10 

and 11 and Figure 1). 

Current Clinical Guidelines: 

Who Should Be Screened? 

As is often the case, current clinical guidelines on 

screening for short cervix with TVU have not yet 

caught up with the evidence. 8,9,12,15 Although the 

ACOG 2008 Practice Bulletin number 98 found 

Internal os 

External os 

Rachel M. Gutkin, MD, is Maternal-Fetal Medicine 

Fellow, Department of Obstetrics and Gynecology, David 

Geffen School of Medicine, UCLA, Los Angeles, CA. 

Lawrence D. Platt, MD, is Director, Center for Fetal 

Medicine and Woman’s Ultrasound, Los Angeles; and Professor 

of Obstetrics and Gynecology, David Geffen School 

of Medicine, UCLA, Los Angeles, CA. 

Figure 1. Normal cervix visualized on transvaginal ultrasound. 


Screening With Transvaginal Ultrasound for Short Cervix: The Solution to Preterm Birth? 

limited evidence to routinely 

screen with TVU for cervical 

length, a number of studies 

have added to the body of 

evidence that supports TVU 

screening in a larger number of 

patients. 16 ACOG further states 

that an effective screening protocol 

for assessing risk factors of 

PTB has not been established. 

ACOG does support TVU 

screening in patients with a 

history of one or more pregnancy 

losses in the second or 

early third trimesters. Research 

is ongoing regarding the effectiveness 

of TVU screening in 

various populations. 

Studies Supporting Predictive Value 

of Short Cervix on TVU 

The optimal time frame for cervical measurement 

is between 14 and 30 weeks; before or after 

that time period, measurement of cervical length 

as a PTB predictor is not accurate or useful. 2,17 

Cervical length of less than 25 mm has been 

found to have the best predictive accuracy for 

increased risk of PTB. 1,17 

Some of the most important trials that have 

established the evidence for short cervix screening 

are summarized here. 

• Short Cervix on TVU Predicts PTB 

In an important study reported by Iams et al 

for the Maternal Fetal Medicine Network, 

the risk of PTB increases as the length of 

the cervix decreases as measured by TVU. 1 

While this was not the first trial showing 

this important relationship, it was the first 

to establish that the length of the cervix is 

directly correlated with the duration of pregnancy—the 

shorter the cervix, the higher the 

risk of PTB. 

• TVU Is Better Than Manual (Digital) Exam 

Cervical length measured by TVU has been 

shown to be a better predictor of PTB than 

The optimal time frame 

for cervical measurement is 

between 14 and 30 weeks; 

before or after that time 

period, measurement of 

cervical length as a PTB 

predictor is not accurate 

or useful. Cervical length 

of less than 25 mm has 

been found to have the 

best predictive accuracy for 

increased risk of PTB. 

cervical length measured 

by manual examination 

in a study of singleton 

pregnancies at high 

risk for PTB that were 

followed from 14 to 30 

weeks. 3 TVU was more 

predictive of PTB, most 

likely because manual 

examination is more subjective 

and has a high 

interobserver variability. 

• TVU Is Very Effective at 

Predicting PTB 

In a retrospective cohort 

study, a short cervix seen 

on a second-trimester 

sonogram was a strong 

predictor of PTB. Almost 

50% of patients with a cervical length of 

15 mm or less had an early spontaneous 

preterm delivery. 18 

• TVU Is Best in High-Risk Patients 

Short cervix on TVU is a better predictor of 

PTB in high-risk patients than in their lowrisk 

counterparts. The sensitivity is greater 

than 50% with a positive predictive value of 

45% between weeks 14 and 18. 3 The populations 

that will most benefit from screening 

are those with prior PTB, multiple gestations, 

uterine anomalies, prior LEEP or cold knife 

cone, multiple prior D&Es, or those with 

symptomatic preterm labor. 16 

• Benefit of Serial TVU Screenings 

High-risk women may benefit from several 

screenings, ie, one at 15 weeks and one at 

18 weeks, although the optimal interval for 

repeat TVU has not been established. 3 

• TVU in Special Situations 

In a recent trial, screening in asymptomatic 

high-risk women predicted spontaneous PTB 

at less than 35 weeks. 19 In another recent trial, 

it was shown that women with a history of 

PTB with preterm labor and intact membranes 

at onset of labor have shorter cervices 


Gutkin • Platt 

Funnel 

Short 

cervix 

Cerclage 

stitches 

Figure 2. Funneling. 

Figure 3. Cerclage in cervix. 

than women with a history of PTB and 

preterm premature rupture of membranes at 

the onset of labor. Both groups had shorter 

cervices than low-risk controls 

(Figure 2). 20 

Should Low-Risk Patients 

Be Excluded From TVU 

Screening? 

At the current time, low-risk 

populations (such as low-risk 

singleton pregnancies) are 

excluded from screening. The 

reasons often cited not to 

incorporate low-risk women 

are low positive predictive 

value, the lack of preventive 

therapy, and the cost of TVU. 

Arguments against using low predictive value as 

an exclusion criteria, however, include the fact 

that ultrasounds for genetic abnormalities are 

routinely performed with even lower sensitivity. 

Most low-risk women undergo genetic ultrasound 

examinations during 16 to 23 weeks. A 

TVU may be performed at time of these scans. 

This additional technique would add little 

time and may be of benefit in the reduction 

of prematurity. Perhaps the most persuasive 

argument that TVU should not be limited to 

Perhaps the most 

persuasive argument 

that TVU should not 

be limited to high-risk 

women, such as those 

with a previous preterm 

delivery, is that these women 

contribute only 30% of 

total spontaneous PTB. 

high-risk women, such as those with a previous 

preterm delivery, is that these women contribute 

only 30% of total spontaneous PTB. 21 

Clinical Management 

of At-Risk Patients 

The lack of patient management 

tools available to prevent 

PTB once a short cervix 

has been found on TVU is 

frustrating. Use of tocolytics 

is limited in the absence of 

uterine contractions. Home 

uterine activity monitoring 

and antibiotics are also 

employed sparingly. Bed rest 

now appears to be the main 

intervention utilized. Cerclage 

and pessaries are also used when deemed 

appropriate (Figure 3). 

Cerclage does not prevent PTB in all women 

with short cervical length on TVU. 22 A metaanalysis 

showed that some populations may benefit 

from cerclage (singletons with history of preterm 

delivery), but in others it may have no effect on 

outcome or even be detrimental (twin gestations). 

Overall, cerclage was not associated with any 

effect on PTB in patients with a short cervical 

length determined by TVU. 22 New evidence sug- 

The The Female Patient NEWSLETTER Supplement Supplement November OCTOBER 2008 2009


Effective Technique for Ultrasound of the Cervix 

A 

normal cervical length is considered to be between 

1 and 2 inches (25 to 50 mm). Thus, a short cervix 

is usually considered to be less than 25 mm. 

While transvaginal ultrasound (TVU) is now considered the 

gold standard for cervical measurement, other techniques 

are still currently in use. What are the drawbacks? 

Transabdominal Ultrasound 

Transabdominal ultrasound (TAU) was the original method 

of visualizing the gravid cervix, but it has the limitation of 

being optimally utilized with a full bladder, which is necessary 

to eliminate fetal parts from obscuring the cervix. 10 

This can lead to artificial elongation of the cervix, masking 

of funneling, and the potential for a dilated internal 

os to appear closed. In addition, the external os can be 

difficult to identify with this method. Furthermore, manual 

pressure may be required, due to the distance of the 

cervix from the TAU probe, which can affect assessment. 

Because of these drawbacks, many cases of short cervix 

are missed with TAU (Figure 4). Thus, the role of TAU is 

limited, and experts agree that clinical decisions should 

not be made based on TAU alone. 

Despite these drawbacks, if TAU is the only option in a 

clinical situation, or if the patient declines TVU, screening 

by TAU is still preferable to manual examination 

alone. If the cervical length is less than 30 

mm or if the cervical length cannot be well visualized, 

then it is imperative to refer for TVU. 

when compared with the transvaginal approach. In cases 

where the cervix is successfully visualized, translabial 

cervical lengths have been shown to correlate well with 

those obtained transvaginally. 11 We personally find this 

technique more cumbersome and have reserved this 

mainly for patients with ruptured membranes. Overall, 

TVU is the superior method. The same caveats apply to 

TLU as to TAU regarding patient management. 

Transvaginal Ultrasound 

Most clinical trials conducted over the past 10 years 

examining short cervix and preterm birth (PTB) have used 

TVU successfully, leading to the recognition of TVU as 

the gold standard for cervical length evaluation. TVU provides 

the best cervical visualization without obstruction, 

and bladder filling is not required. In fact, we prefer to 

have an empty bladder. TVU is safe, easy for the health 

care professional to perform, and the technique has high 

patient acceptability. 

Technique for Performing TVU 10,12 

Operators should have completed 50 or more procedures 

to become proficient. Less than accurate measurements 

may result if the bladder is partially full, if excessive probe 

Translabial Ultrasound 

Translabial ultrasound (TLU) has been used 

because visualization is not obstructed by fetal 

parts, bladder filling is not required, and visualization 

is improved in comparison to TAU, due to 

the closer proximity of the probe to the cervix. 

However, even with these improvements, the full 

length of the cervix is visible in only 80% of cases 

Figure 4. Transabdominal vs transvaginal ultrasound scans. 

gests that therapeutic cerclage placement may be 

more efficacious in patients with shortened cervix 

who have a history of a prior term rather than a 

prior preterm delivery. 23 

With regard to pessary usage in the setting of 

shortened cervix, there are limited data in American 

publications. Several European studies have 

suggested a possible role for this noninvasive device. 

Additional studies must be performed to evaluate 

the efficacy of pessaries for this indication. 

ACOG advises that when a short cervix is present, 

assessment should be made for potential fetal 

anomalies, uterine activity should be evaluated, and 

maternal chorioamnionitis should be excluded. 8 It 

is reasonable to suggest that performing TVU in 

isolation without performing a detailed fetal anat- 

10 The Female Patient Supplement OCTOBER 2009

Gutkin • Platt 

Figure 5. Effect of probe pressure. 

pressure is applied, if the cervix is curved, or if uterine 

contraction occurs during the examination (Figure 5). 

The patient should have an empty bladder. The 

probe should be covered with a single-use latex (or 

nonlatex if the patient indicates 

Funnel 

latex allergy) disposable sleeve. 

The probe is inserted (some 

patients prefer to insert it themselves), 

and a sagittal view of 

the cervix is visualized when the 

probe is in the anterior fornix. 

The probe is then withdrawn 

until the image is blurred. Light 

pressure is then applied, just 

enough to see the cervix clearly, 

at which point the image is 

enlarged to fill two-thirds or 

more of the screen. This is the 

stage at which the measurement 

is taken. Measurement from the external os to 

the internal os along the endocervical canal is taken. 

Several measurements are obtained, using the shortest 

as the best. Some operators obtain another set of 

measurements after applying transfundal pressure with 

the hand for 15 seconds. Little extra time is required for 

this entire process. 

Funneling and Other Anomalies 

The risk of PTB is also correlated to funneling 

(Figure 6). This is due to the fact that funneling, 

or dilation of the internal os, is part of the 

process of cervical shortening. However, due 

to its interobserver variability, funneling is less 

reproducible than cervical length. It has been well 

documented that funneling is not a predictor of an 

increased risk for PTB when it is associated with 

a long cervix. 13 

Lower uterine contraction can mimic funneling, 

but the echogenicity is different. The examination 

should continue to monitor the cervical appearance 

after the contraction disappears. If the 

contraction remains throughout the exam, the patient 

should be reevaluated in 1 to 2 days to monitor for 

resolution of the contraction. 


cervix 

Figure 6. Funneling with shortened 

cervical length. 

Funnel 

Sludge 


cervix 

Figure 7. Amniotic fluid sludge. 

Amniotic fluid sludge has also been reported as an 

independent risk factor for PTB. In association with shortened 

cervical length, studies have correlated it with a 

higher risk for PTB than the risk found with either variable 

alone. 14 Further research regarding the significance of 

sludge and its origin is needed to determine the significance 

of this finding on TVU (Figure 7). 

omy scan is insufficient. In addition, if not already 

made, lifestyle changes should be implemented 

that would affect PTB, including smoking cessation, 

moderation of activity, and discontinuation of 

coitus. ACOG further advises that because of the 

lack of evidence for the effectiveness of cerclage, 

elective cerclage should be reserved for patients 

with a history of 3 or more early pregnancy losses 

or PTBs. 8 Studies are ongoing to reevaluate the 

efficacy of cerclage, so a different approach cannot 

be recommended until trial results are available. 

While cerclage still has a place as an intervention, 

other possible interventions, such as treatment 

with progesterone, are on the horizon. 

While ACOG recommends that progesterone be 

offered to women with a prior singleton PTB, the 

The The Female Female Patient Patient NEWSLETTER Supplement Supplement OCTOBER 2009 11


drug is not yet FDA-approved for this indication. 9 

Several current trials are investigating the efficacy 

of progesterone for the prevention of PTB. 

Conclusion 

Short cervix measured by TVU is the most accurate 

screening tool currently available to predict 

PTB. Its use is safe, effective, reproducible, and 

acceptable in all studied populations. A cervical 

length of less than 25 mm when found on TVU 

between weeks 14 and 30 is highly predictive 

of PTB. It is our own practice to monitor with 

increased surveillance patients who have cervical 

length less than 30 mm during this time period. 

The need for effective interventions is critical. 

While bed rest and cerclage are currently the main 

interventions available, studies are in progress that 

may point to progesterone as an option. 

References 

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12 The Female Patient Supplement OCTOBER 2009

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