Influence of cut‐off value on prevalence of short cervical length

Abstract

A cut-off value of 30 mm for CL was used to include women in a randomized clinical trial that was embedded in a cohort study. We suggest that the use of a predefined cut-off value for a short cervix influences the distribution of the CL measurements. Since the measurement is not blinded, preference of assessors for the control or intervention arms may have introduced selection bias. This might have resulted in fewer measurements around the cut-off value. Other trials using similar designs could benefit from this observation and take precautions to avoid selection bias. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Midtrimester Cervical Length in Low-Risk Nulliparous Women for the Prediction of Spontaneous Preterm Birth: Should We Consider a New Definition of Short Cervix?

“…When the measurement is not blind, the use of a predefined cut-off value could influence the distribution of the CL measurements. 31 Our study also confirms that smoking during pregnancy is associated with increased risks of sPTB. 32 The low prevalence of smoking in our population may in part explain the low incidence of sPTB.…”

“…On the other hand, it is important to mention the important study of Celik et al who observed a significant correlation between CL at 20 and 24 weeks, and sPTB at less than 28, 32, 34, and 37 weeks of gestation in 58,807 women from all parities. 29 Of note, they observed a median (inter-quartile range) CL of 30 mm (23-35), 31 mm (25-36), and 33 mm (28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38) in women who had a sPTB between 28 and 30, between 31 and 33, and between 34 and 35 weeks of gestation, respectively, compared with 35 mm (31)(32)(33)(34)(35)(36)(37)(38)(39)(40) in women who delivered at term (p < 0.001). However, the participants and physicians were not blinded to the results, and several women underwent cervical cerclage or received progesterone, which could have influenced the results.…”

The Impact of Routine Transvaginal Ultrasound Measurement of the Cervical Length on the Prediction of Preterm Birth: A Retrospective Study in a Tertiary Hospital

“…35 Nowadays, there is no debate that second-trimester TUCL is the most powerful screening instrument available, but the best cut-off to separate normal from short cervixes is still controversial. 16,[19][20][21][22][23] As most parameters in medicine, there is no biological TUCL cut-off, and defining "short" is not an easy task. Lower cut-offs present good specificity but low sensitivity, but higher values (like 29 mm) lead to an increase in the false-positive rate.…”

“…17,18 The risk of experiencing PTB is inversely correlated to the cervical length, but the ideal cut-off for clinical use is still controversial. 16,[19][20][21][22][23] By definition, a cervical length below the 10th centile for gestational age is considered "short." This value varies according to the gestational age, the populational distribution of TUCL, and the prevalence of PTB.…”

Repeated cervical length measurements for the verification of short cervical length

“…A limitation of the study was that a repeated cervical length measurement was only performed in patients with initial measurements of 30 mm or shorter and that, in the present study population, a 'dip' of cervical length measurements between 20 and 30 mm was observed, probably as a result of the fact that assessors were not masked. 15 Consequently, partial verification bias could have been present. However, this mainly affected women who were incorrectly classified as low-risk; this could only have led to an underestimation of the effect of cervical length on preterm delivery.…”