1. Perinatal Quality Foundation (perinatalquality.org)
How to Measure Cervical Length
Perinatal Quality Foundation (perinatalquality.org)

2. Outline
Normal Cervix Standard Cervix Image Criteria Transvaginal Examination Techniques Cervix Mobility Considerations Cervical Length Examination Protocols and Sequence Cervical Measurement Pitfalls References

3. Standardization  Reliability
Reliable cervix measurements during screening are required to achieve the potential of reduced preterm births.
Reliable cervix measurements require:
Standard image criteria
Consistent examination protocols

4. I. Standard Image Criteria

5. Measurement of the Cervix
Funnel
Length
Cervical
Length
Record
B as
THE Cervical Length B A
A is the
Funnel
Length.
B is the
Cervical
Length CA CP
C Ant Lip should = C Post Lip
Berghella, Ultrasound Obstet Gynecol 1997;10:161
Burger, Ultrasound Obstet Gynecol 1997;9:188

6. Normal Cervix Posterior Cervix Internal Os Fetal Head Bladder Ext Os
Empty
Ext Os
Internal Os
Fetal
Head
Posterior
Cervix

7. Cervical Screening Measurement Image Criteria
Transvaginal Image
Cervix ~ 75% of the image
Anterior = Posterior Width
Maternal Bladder Empty
Internal Os Seen
External Os Seen
Cervical Canal Visible throughout
Caliper Placement Correct
Cervix Mobility Considered

8. Criteria 1: Transvaginal (TVU) Image
Transabdominal Image
CL = 37 mm.
Transvaginal Image
Same patient
CL = 25 mm.

9. Transvaginal Cervical Sonography
The next series of slides repeats some slides in earlier Sections to illustrate how new information about cervical function has required a reassessment of traditional theories about the pathogenesis of preterm birth. This reassessment is still underway and forms the basis for much of the current research agenda.
One of the first areas of inquiry that prompted a re-evaluation of traditional thinking was investigation of the process of cervical change using endovaginal sonographic images of the pregnant cervix. This cartoon shows the endovaginal probe in the anterior fornix and the corresponding sagittal view of the cervix.
What is Wrong with This Picture?
Illustration by James Cooper MD
Berghella, in Callen 5th edition 2008.

10. Transvaginal Ultrasound (TVU)
No imaging barriers between transducer and cervix
Empty bladder is exam standard
Safe, comfortable, well-accepted
Easier than trans-perineal imaging
The Gold Standard
Add TVU sequence
TVU provides even better visualization of the cervix, since there’s no obstruction, and no required bladder filling. It has been shown to be safe, confortable and well-accepted by patients, and easier than TL. Therefore it has become the gold standard ultrasound technique
I particularly like the abbreviation TVU for transvaginal ultrasound, since it describes graphically the progression of cervical shortening and opening from the normal T appearance to V and then U (point)
Berghella, Clinical Obstet Gynecol 2003;46:947

11. AIUM Guidelines for Transvaginal Probe Care
The endocavitary probe should be covered with a barrier (condom or probe cover). Users need to be aware of latex sensitivity and have non-latex barriers available. Users should wear gloves throughout the procedure. Care should be taken to clean hands and surfaces after the procedure.
AIUM Guidelines for Cleaning and Preparing Endocavitary Transducers Between Patients, 2003.

12. AIUM Guidelines for Transvaginal Probe Care
The probe should be cleaned with soap and water immediately after the procedure. High-level disinfection of the probe is required between patients. Allot the time specified on the product label for high-level disinfection. FDA has published a list of high level disinfectants for use in processing reusable medical devices. That list may be consulted to find agents that may be useful for probe disinfection.
AIUM Guidelines for Cleaning and Preparing Endocavitary Transducers Between Patients, 2003.

13. Trans-Abdominal (TAU) Pitfalls
Fetal parts may obscure cervix
Bladder filling may elongate cervix and mask funnel
Long distance from probe decreases resolution
Manual pressure may compress lower uterine segment and mimic cervix

14. Can the Cervix Be Measured with Transabdominal Ultrasound (TAU)?
Bladder volume has unpredictable effect on cervical length Mason, BJOG 1990;90:457
CL by TAU > TVU and not reliable To, Lancet 2004;363: Hernandez-Andrade, J Maternal-Fetal Neonatal Med 2012;
CL by TAU = TVU after training period Saul, J Ultrasound Med 2008;27:1305
CL by TAU < TVU and therefore reliable Stone, Aust N Z J Obstet Gynaecol 2010;50:523
Accuracy of TAU differs significantly according to whether a patient has a short cervix or a normal cervical length Hernandez-Andrade, J Maternal-Fetal Neonatal Med 2012:
Transabdominal evaluation is the least reliable method ACR Appropriateness Criteria: Assessment of the Gravid Cervix, 2011.

15. Reasons Not to Screen by TAU
Sensitivity of TAU for preterm birth is 8% Iams, N Engl J Med 1996;334:567 Owen, JAMA 2001;286:1340 Short Cervix missed on TAU Rust, Am J Obstet Gynecol 2001;185:1098 To, Lancet 2004;363:1849 Althusisius, Am J Obstet Gynecol 2001;185:1106 Fonseca, N Engl J Med 2007;357:462 Hernandez-Andrade, J Mat-Fetal Neonatal Med 2012; Major studies & RCTs over >10 years have all used TVU

16. Reasons Not to Screen by TAU
Transabdominal US measurement of cervical length was unable to identify 57% of cases with a short cervix (<25mm) as determined by transvaginal US. Transvaginal US cervical measurements were more reproducible than transabdominal US. Transabdominal US did not detect sludge and funneling in all cases. Transabdominal measurement overestimated cervical length by 8mm among women with a short cervix and underestimated cervical length among women with a normal cervix. The accuracy of transabdominal US differs according to whether a patient has a short cervix or a normal cervix.
Hernandez-Andrade, J Maternal-Fetal Neonatal Med 2012:

17. Criteria 2: Cervix Occupies 75% of the Image

18. Cervix Doesn’t Occupy 75% of Image

19. Cervix Doesn’t Occupy 75% of Image
Note previa in notes
This image demonstrates a placenta previa and a measurement from the internal os to the placental edge.

20. Criteria 3: Anterior Width = Posterior Width

21. Criteria 3: Anterior Width = Posterior Width
The anterior cervical thickness is equal in width to the posterior cervical thickness .
The echogenicity is similar both anterior and posterior.
There is minimal concavity created by the transducer.

22. Anterior Width ≠ Posterior Width
NT is only seen on a small part of the fetal dorsum.
Note increased echogenicity anterior portion of cervix

23. Anterior Width ≠ Posterior Width
NT is only seen on a small part of the fetal dorsum.
Prominent concavity at transducer face

24. Anterior Width ≠ Posterior Width
NT is only seen on a small part of the fetal dorsum.
Prominent concavity at transducer face

25. Criteria 4: Empty Maternal Bladder

26. Maternal Bladder Not Empty
NT is only seen on a small part of the fetal dorsum.

27. Maternal Bladder Not Empty
NT is only seen on a small part of the fetal dorsum.

28. Criteria 5 & 6: Internal and External Os Well Seen

29. Criteria 5 & 6: Internal and External Os Well Seen

30. Pitfall: Uterine Contraction
Contractions may obscure the internal os & mimic funneling

31. Pitfall: Uterine Contraction

32. Pitfall: Uterine Contraction
NT is only seen on a small part of the fetal dorsum.

33. Neither Os Seen Well 
NT is only seen on a small part of the fetal dorsum.

34. Too much pressure: Neither os seen well

35. External Os Not Well Seen
NT is only seen on a small part of the fetal dorsum.

36. Internal Os Not Clear 

37. Criteria 7: Cervical Canal Completely Visible Throughout
Note previa in notes

38. Cervical Canal Visible Throughout
This
is an
example
of an
exception
to the
bladder
edge
being
directly
above the
internal os

39. Cervical Canal Not All Visible
NT is only seen on a small part of the fetal dorsum.

40. Cervical Canal Not Visible Throughout
NT is only seen on a small part of the fetal dorsum.

41. Criteria 8: Caliper Placement Correct
Bladder
Ext Os
Int Os
Fetal
Head
Posterior
Cervical Lip

42. Caliper Placement is Correct

43. Where to Put the Calipers?
Where the anterior & posterior walls of the canal touch
Not outer-most edge
Spend enough time to see whether a small echolucent area is stable, or is going to open up
YES NO

44. B = Funnel A = Cervix Length
Cervix Length  A + B

45. Caliper Placement Incorrect
Remember not to include funnel in Cervix length measurement

46. Caliper Placement Incorrect

47. How to Measure a Curved Cervix: Don’t Trace to Measure the Cervical Length
Why Not?

48. How to Measure the Curved Cervix: Use Multiple Measurements

49. How to Measure the Curved Cervix: Use Multiple Measurements

50. Criteria 9: Cervix Mobility Considered
The Cervix is Dynamic
Examinations must take cervical changes into account

51. Local Contraction - Single ExaminationCL
33 mm CL
7mm
Clue = Debris
Guzman, Obstet Gynecol 1998;92:31

52. Dynamic Technique Withdraw probe until blurred / Reapply
Enlarge image (2/3 of screen)
Measure Ext Os  Int Os along endo-cervical canal
Apply fundal or suprapubic pressure
Obtain 3 measurements, use shortest best
Total exam time about 5 minutes
We then withdraw the probe until the image blurs, then reapply just enough pressure to obtain a clear view of the cervix, which we enlarge to 2/3 or more of the screen (point). The measurement of cervical length is obtained fro the e. to the I.o. along the endocervix. We obtain at least 3 measurements, using after review the shortest best for the report. Then TFP is applied, and measurements taken again. The examination lasts an average of approx. 3 to 5 minutes.
I cannot stress enough how critical it is to ensure proper technique in order to obtain valid data and avoid errors.
Berghella, Clin Obstet Gynecol 2003;46:947

53. II.Consistent Examination Protocols

54. Quality Operator Considerations
Experience w/ Transvaginal Exams Recent Education in Standard Cervical Image Criteria Practice in obtaining symmetrical cervical imaging (50 or more exams before proficient studies) Documentation of Inter-observer variability of 7-10% or less
Symmetric image of cervix should be obtained
To obtain such adequate technique, one needs to do 50 or more procedures before being proficient
Burger, Ultrasound Obstet Gynecol 1997;9:188
Berghella, Ultrasound Obstet Gynecol 1997;10:161

55. Pre-exam Considerations
Check the equipment
Transducer appropriately cleaned w/ soap & water + soaked for sufficient time for high-level disinfection
Use standard 5 to 7 MHz endovaginal probe
Use the “EV” EndoVaginal setting (Not OB or ABD)
Ask patient about latex sensitivity
Empty maternal bladder
Void just before the exam
If bladder is seen to be large, stop exam & void again

56. Transvaginal Exam Considerations
Some women prefer to insert probe themselves Guide along anterior fornix for sagittal view of cervix Look in top ½ of image for maternal bladder & AF Find these landmarks in sequence: Amniotic Fluid & Fetus  then Bladder  Internal Os  Cervical Canal, and then  External Os Rotate probe to see best long axis view of the canal Withdraw probe until image blurs to reduce compression from the transducer, then …
Proper techinque is extremely important, as is for Doppler or nuchal translucency measurements, to obtain reliable data.
The technique of TVU includes having the patient empty her bladder, letting her insert the condom-covered probe in the anterior fornix, to obtain a sagittal view of the cervix ….

57. Measurement Technique
Relax probe pressure until image begins to blur, then reapply just enough pressure to create best image
Visualize standard criteria
Measure CL repeatedly until  is < 10%
Record the “Shortest Best Measurement”
Discard poor measurements – Do Not Average

58. Reporting Considerations
What is “Shortest Best” ?
Take repeated measurements until you get 3 that all meet criteria (anterior = posterior thickness, landmarks seen) that vary by < 10%
Of these 3 excellent images, record the SHORTEST one – not the one you think is “prettiest” – we want to minimize subjective variation

59. Trouble Finding a Good Image?
Start over by relaxing pressure & finding landmarks
Find lowermost edge of the empty bladder – internal cervical os should be directly below
Cx axis may not lie in mid-plane of torso
Image should fill 75% of the screen

60. Cervical Scan Technique
1st measurement may be longer than subsequent measurements  Discard it
Apply pressure to find funnel and assure best measurement
Use mild fundal and then suprapubic pressure
Remember to reduce probe pressure while fundal and suprapubic pressure applied

61. Summary
Standard Image Criteria
Consistent Examination Protocols

62. Technique Empty maternal bladder.
Using TVU find the internal os, external os, cervical canal and endo-cervical glands.
Avoid undue pressure on the cervix.
Anterior width = Posterior width.
The cervix should occupy > 75% of the image.
Measure the closed portion of the cervix.
Perform 3 measurements over > 3 minutes.
Record the Shortest length that Meets Criteria.
Not the average length, and Not the prettiest picture

63. TVU Pitfalls
Technical Full bladder Too much pressure Failure to visualize entire cervical length Incorrect caliper placement Exam too short to visualize dynamic cervix changes Anatomic Contraction Underdeveloped LUS

64. Other Factors Affecting Cervical Measurement
Gestational age:
Lower segment of uterus may be difficult to distinguish from cervix until somewhere between 16 and 20 weeks
If can’t tell at 16-18, ask her to come back at wks
Maternal bladder volume always an issue – empty it
Duration of scan – A scan < 3 minutes is inadequate
OPERATOR experience & training
Set aside whatever you were taught
We all have to measure the cervix the same way.

65. For further information