[CG] Transvaginal ultrasound evaluation of the cervix - measurement of cervical length


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  1. The probe should be placed in the anterior fornix of the vagina
  2. The maternal bladder should be essentially empty.
  3. A sagittal view of the cervix should be obtained with confidence.
    Remember that the longitudinal axis of the cervix often does not lie exactly within the maternal sagittal axis.
  4. The amount of pressure exerted with the transducer should be kept to a minimum to avoid artificially lengthening the cervix.
  5. The widest viewing angle of the available ultrasound field should be used.
  6. The sonolucent endocervical mucosa should be identified as a guide to the true position of the internal os. The callipers should be placed to measure the linear distance between the triangular area of echodensity at the external os and the V-shaped notch at the internal os.

  1. The presence of funnelling should be noted but attempts should not be made at trying to measure it.
  2. The shortest cervical measurement should be recorded rather than an average of the measurements obtained.

Sonek j and Shellhaas C. Cervical sonography a review. Ultrasound in Obstetrics and Gynaecology, 1998;11:71-78

To MS, Skentou C, Chan A, Zagaliki A and Nicolaides KH. Cervical assessment at the routine 23 week scan: standardising techniques. Ultrasound in Obstetrics and Gynaecology 201; 17:217-219

Last reviewed: 24 August 2017

Next review: 24 August 2022

Author(s): Dr. M.A. Ledingham Consultant Obstetrician, SGH; Carole Murray, Lead Sonographer, Glasgow; Dr. A. M. Mathers, Consultant Obstetrician on behalf of GONEC Group

Reviewer Name(s): Donna Bean