Three-dimensional Ultrasound in the Second Stage of Labour

Caesarean sections in the second stage of labour are on the rise globally and a significant proportion is due to the inadequacy of clinical assessment of the relationship between the fetal head and the maternal pelvis structures and the influence this has on the selection of the mode of delivery. Ultrasound technology has rapidly advanced over the last 40 years, so much so that the application of the three-dimensional (3D) ultrasound can now be considered in the management of the second stage of labour. Extensive work has been done to establish criteria for the assessment of the fetal head descent and the relationship it has to the maternal pelvic structures in the second stage. The development of intrapartum translabial ultrasound (ITU) measurements such as the "angle of progression" measurement has been proven to help in the selection of patients who will benefit from a trial of spontaneous delivery or operative instrumental delivery while on the other hand identifying those patients who may benefit from a caesarean section when the measurements are not favourable. It is in this regard, where the clinical application of the ITU is playing an emerging role in influencing the clinical outcomes of patients in the second stage of labour. Further to this, the use of new advanced computer software using multiplanar mode acquisition techniques can generate 3D images and volume measurements from two-dimensional parameters to assess the progress in labour and the second stage of delivery. There are several benefits to this. Firstly, an objective assessment of the fetal head relationships can be documented, detailing not only descent but also flexion, rotation and aspects asynclytism which are all important, especially, where an operative delivery is being considered. Secondly, the risk of ascending intrapartal infection may be reduced as internal examinations are less frequent. Finally, the ITU is not as invasive a procedure as an internal examination.

Keywords: Angle of progression, Intrapartum, Labour, Second stage, Threedimensional ultrasound.