In February 2011, the Society for Maternal-Fetal Medicine, at its Annual Clinical Meeting, held a debate session. One of the topics debated was whether or not cerclage should be performed in women with a prior preterm birth and a short cervix on ultrasound. My position in that debate was the contrary one (no surprise to those who know me). Beyond a healthy skepticism the facts are needed in order to properly answer this question, so what are the facts?

If one considers obtaining a patient’s history as an “interview” then there is precedent regarding the uncertainty of information obtained in this way leading to a desire to use some more “objective” measure, in this case ultrasound. There are 2 key aspects of such an “objective” test, namely accuracy (or validity) and variability, reproducibility (or precision). Two ways to measure accuracy involve the measurement of sensitivity and specificity. With respect to ultrasonographically determined cervical length, the sensitivity is low as is the positive predictive value (9.3-25.7%). If one were to strictly apply epidemiologic principles to the dilemma of the short cervix and its possible association with preterm delivery the following conclusions could be reached:

• 1
  

  The association may be more indirect than direct.

  
  
• 2
  

  Consistency of association is lacking–frequently the case if a disease, in this case prematurity, is caused by multiple factors.

  
  
• 3
  

  Strength of association is lacking–ie, the relative risks, especially in the groups with a cervical length <25 mm have been inconsistent.

  
  
• 4
  

  Specificity of association is difficult to establish due to the multifactorial nature of preterm birth.

  
  
• 5
  

  Degree of exposure, or so-called “dose response,” does seem to favor the short cervix as being involved in preterm birth since, as Iams et al has pointed out, the length of the cervix may (or should) be viewed as a continuum, and the data do suggest that as the cervix shortens (down to even 0 cm) the risk of preterm delivery increases.

Lastly, maternal-fetal medicine specialists are in a unique and uncomfortable position. We are the ones who take the history, perform the ultrasounds, recommend (and often perform) the cerclage, and for the latter 2 of these activities are reimbursed, so is it possible to be entirely objective when making recommendations? Who should be the final arbiter? My opinion is that it should be “us,” but prior to making cerclage “standard of care,” a phrase our legal colleagues use liberally, we owe it to ourselves and to our patients to await the results of well-powered clinical trials–a conclusion also reached by my esteemed colleague Dr Berghella in 2005.