Volume 200, Issue 5 , Pages e37-e39, May 2009
Blinded comparison of cervical portio length measurements by digital examination vs Cervilenz
Article Outline
Objective
Cervical length (CL) examinations may identify patients in preterm labor or those who may benefit from prophylactic therapy. We sought to compare the accuracy of clinician digital CL examinations with objective measurements using the Cervilenz device in women presenting with symptoms of preterm labor.
Study Design
Forty-two patients with singleton gestation from 24 to 34 weeks' gestation and cervical dilation less than 3 cm underwent speculum examination and Cervilenz measurement. A second examiner, blinded to results, digitally measured CL. Pearson's correlation coefficient, Student t tests and McNemar's tests were used to compare digital and Cervilenz measures.
Results
Digital CL was significantly less than Cervilenz (2.88 vs 3.40 cm; P < .001), and in 36% of subjects, this difference exceeded 1 cm. The discrepancy in CL estimates persisted whether women were multiparous or had soft cervices or a history of preterm delivery.
Conclusion
Digital assessment underestimates CL, whereas the Cervilenz device permits a visualized and objective CL measure in patients with preterm labor.
Key words: cervical length, Cervilenz, preterm labor, vaginal examination
Preterm birth complicates approximately 12% of pregnancies, accounting for 70% of neonatal morbidity and mortality.1, 2 Preterm labor (PTL) precedes the majority of these births. Because 80% of presumptive preterm labors will not result in preterm delivery,3 there is concern that the diagnosis of PTL is inappropriate in many patients.
The criteria for PTL include uterine contractions that evoke demonstrable effacement and dilation of the cervix. In early PTL, a change in cervical length (CL) or effacement commonly precedes a change in dilation. In these patients, CL is most often assessed by digital cervical examination, a semisubjective procedure that is flawed by significant interobserver variability.4 Nevertheless, accurate CL measurement is essential for decisions regarding hospitalization and/or therapy.
Cervilenz is a low-cost screening tool for objectively assessing cervical portio length. It is a disposable measuring probe with a movable flange to measure the distance from the lateral fornix to the distal end of the cervix under direct visualization.5 The present study was undertaken to evaluate the correlation between CL measured digitally and with Cervilenz and evaluate whether labor factors including multiparity, cervical consistency, or history of preterm delivery influenced these measurements.
Materials and Methods
The study was approved by the institutional review board of Harbor-UCLA Medical Center. Informed consent was obtained from women presenting to labor and delivery with suspected preterm labor between 24 and 34 weeks' gestation. CL measurement was evaluated as part of a study of suspected PTL. Inclusion criteria included uterine contractions, cervical dilation less than 3 cm, intact membranes, and singleton gestation.
At study entry, subjects underwent a 2-step evaluation to measure CL during periods of uterine quiescence. First, during speculum examination, CL was measured with the Cervilenz device to the nearest 0.1 cm. A second physician, blinded to the Cervilenz result, measured CL by digital examination to the nearest 0.1 cm. All treating physicians were residents (postgraduate year 2-4) who underwent training to measure Cervilenz CL using vaginal models and to assess digital CL by comparing their estimated CL with a measuring tape on their examining digit.
Additional factors evaluated included maternal age, parity, gestational age, ethnicity, history of preterm delivery, and cervical consistency (soft, medium, or firm). Correlation between digital CL and Cervilenz CL measurements was evaluated using Pearson's correlation coefficient. The mean CL was calculated for the entire group and subgroups (eg, multiparity, nulliparity). The paired Student t test was used for comparison of digital CL and Cervilenz CL within the same patients, whereas the upaired Student t test was used for comparison of the mean absolute difference between digital CL and Cervilenz CL among groups of patients (eg, multiparous vs primiparous). Proportions of patients with digital CL greater than vs less than Cervilenz CL were compared with the McNemar test. Statistical significance was established at P < .05.
Results
There were 42 study subjects, with maternal age of 27.6 ± 7.2 years and gestational age of 30.5 ± 2.8 weeks. The majority were multiparous (64%) and Hispanic (71%), whereas one third had a prior preterm delivery and 38% had soft cervical consistency.
Digital CL did not correlate with Cervilenz CL measurements (r = 0.13; P = .40; Figure). Mean digital CL was significantly less than Cervilenz CL (2.88 ± 0.70 vs 3.40 ± 0.67 cm; P < .001), with mean absolute difference of 0.89 ± 0.08 cm. This was due to the fact that digital measurements were more often shorter, as opposed to greater, than those taken with Cervilenz (69.1% vs 28.6%; P < .001). In 36% of subjects, the digital CL measured 1.0 cm or greater shorter than the corresponding Cervilenz CL.
FIGURE.
Correlation between Cervilenz CL and digital CL measurements
Y = X line is displayed for comparative purposes.
Burwick. Cervical portio length measurements by digital examination vs Cervilenz. Am J Obstet Gynecol 2009.
Significantly shorter digital CL compared with Cervilenz CL measurements persisted in subgroups of women with soft (2.65 ± 0.83 vs 3.36 ± 0.89 cm; P = .016) or medium-firm cervix (3.01 ± 0.59 vs 3.44 ± 0.52 cm; P = .013), nulliparous (2.89 ± 0.76 vs 3.59 ± 0.54 cm; P = .010), or multiparous (2.80 ± 0.76 vs 3.29 ± 0.72 cm; P = .025) and in those without a history of preterm delivery (2.98 ± 0.56 vs 3.55 ± 0.55 cm; P = .002).
The mean absolute difference between digital CL and Cervilenz CL measurements was significantly greater in women with soft as compared with medium-firm cervix (1.13 ± 0.14 vs 0.75 ± 0.10 cm; P = .03). The mean absolute difference was not significantly affected by multiparity as compared with nulliparity (0.83 ± 0.10 vs 0.98 ± 0.15; P = NS) or by a history of prior preterm delivery as compared with those without prior preterm delivery (0.90 ± 0.09 vs 0.88 ± 0.15; P = NS).
Comment
This study comparing the semisubjective digital CL examination to the directly visualized, objective Cervilenz measurement confirms the relative inaccuracy of digital examination. The digital CL underestimated cervical length with differences between digital CL and Cervilenz CL 1 cm or greater in 36% of our cohort. These differences persisted in patients with possible confounding factors including soft cervical consistency, history of preterm delivery, and multiparity. Our study suggests that Cervilenz may provide an easy, objective method to measure CL and thus may be an effective screening tool to identify suspected preterm labor patients with a short or shortening CL.
Clinically, digital assessment of cervical length has been the standard screening modality for patients in PTL, but this method has been shown to be semisubjective with large interobserver variability.4 Prospective studies indicate that digital exam only demonstrates good reliability if the level of agreement is defined as 10 mm, a range of error that could have significant perinatal implications. Despite our program of physician education of their individual digit lengths, the digital examination was consistently shorter than Cervilenz examination. Because the study examiners were all residents (postgraduate year 2-4), it is unknown whether more precise digital measurements would be obtained by experienced practitioners.
The Cervilenz CL excludes any nonvaginal portion of the cervix and on average measures 0.35 cm less than transvaginal ultrasound (TVU) CL measurements.5 Of note, Grimes-Dennis and Berghella6 concluded that digital examinations averaged 1.1 cm less than TVU CL measurements. These results are consistent with the present findings that digital assessments were significantly shorter than those of Cervilenz.
In view of the pending report of the National Institutes of Health Maternal Fetal Network cerclage study of patients with a short cervix at 16-22 weeks' gestation and recent publications demonstrating the efficacy of progesterone therapy for patients with a short cervix at 24-28 weeks' gestation, cervical length assessments will likely become incorporated into routine prenatal care. Recently Spong7 stated that “evaluation of the cervical length serially (every 2 weeks) between 16 and 24 weeks of gestation may aid in the identification of increased risk for preterm birth.”
Although TVU remains the gold standard for cervical length assessment, the equipment, training, and cost associated with TVU may be prohibitive if multiple cervical length screens are to be performed in each pregnancy. The use of Cervilenz does not require expensive machinery or advanced training in ultrasound and has the potential to be able to be broadly utilized by obstetric providers, including general obstetrician gynecologists, family practitioners, midwives, and nurse practitioners. Cervilenz may serve as an appropriate screening test to be performed in the obstetricians' office, with those patients identified to be at risk referred for a diagnostic TVU and potential therapy.
In summary, the present study indicates that digital examination results in a clinically significant error in CL measurement in patients with suspected PTL. These results suggest that the use of an objective measure of CL may improve the identification and potentially the treatment of patients with PTL or short cervical length.
Acknowledgment
We thank Margaret Pourtemour, BS, for her assistance in patient recruitment.
References
- . ACOG practice bulletin. Assessment of risk factors for preterm birth. Clinical management guidelines for obstetrician-gynecologists. Number 31, October 2001 (replaces technical bulletin number 206, June 1995; committee opinion number 172, May 1996; committee opinion number 187, September 1997; committee opinion number 198, February 1998; and committee opinion number 251, January 2001). Obstet Gynecol. 2001;98:709–716
- . Management of preterm labor. Number 43, May 2003. Int J Gynaecol Obstet. 2003;82:127–135
- Fetal fibronectin as a predictor of preterm birth in patients with symptoms: a multicenter trial. Am J Obstet Gynecol. 1997;177:13–18
- . Interobserver reliability of digital and endovaginal ultrasonographic cervical length measurements. Am J Obstet Gynecol. 1997;177:853–858
- . Objective cervical portio length measurements (Consistency and efficacy of screening for a short cervix). J Reprod Med. 2007;52:385–389
- . Cervical length and prediction of preterm delivery. Curr Opin Obstet Gynecol. 2007;19:191–195
- . Prediction and prevention of recurrent spontaneous preterm birth. Obstet Gynecol. 2007;110(2 Pt 1):405–415
PII: S0002-9378(08)02246-1
doi:10.1016/j.ajog.2008.11.026
© 2009 Mosby, Inc. All rights reserved.
Volume 200, Issue 5 , Pages e37-e39, May 2009
