Is the current measurement criteria appropriate for selecting women who require transvaginal assessment of cervical length in a low-risk population?

Abstract

Introduction The aim of this study was to assess the number of low-risk women in our population that would require transvaginal examination of cervical length on the basis of current transabdominal screening criteria. Also, if the currently used length of 35 mm transabdominally (at 12–40 weeks gestational age) could be lowered while still accurately identifying all cervical lengths that would be less than 25 mm measured transvaginally. Method Over a 3-month period, all patients presenting for obstetric scanning between 12 and 40 weeks gestation were included in the study. Details to be recorded included sonographer initials, scan date, patient identification number, gestational age, transabdominal cervical length, transvaginal cervical length and relevant risk factors. Patients who were subsequently identified as being high risk for preterm delivery were excluded from the data analysis. Results Recent literature suggests that using a cut-off length of 36 mm transabdominally for a well-visualized cervix will result in a 40% reduction of women requiring transvaginal examinations of cervical length at the mid-trimester scan.[1] Our current practice protocol is to use a similar cut-off of 35 mm measured transabdominally less than which transvaginal assessment of cervical length is indicated. It was found that only 13% of low-risk women in our practice required a transvaginal scan for cervical length (a reduction of 87%) at the mid-trimester scan. At 12–40 weeks gestational age, using a transabdominal cut-off as low as 25 mm would have allowed for the identification of all patients in the study group with transvaginal measurements of less than 25 mm. Discussion Across 12–40 weeks gestational age, an average of 17% of women required transvaginal assessment of cervical length on the basis of current criteria. Allowing for measurement error practice protocol could be amended to using a transabdominal cut-off of 30 mm at all gestational ages when deciding which patients would benefit from transvaginal assessment of cervical length.