Ultrasound in labor: is it time for a more simplified approach?

Abstract

The use of transperineal intrapartum ultrasound assessment has been introduced in recent years to complement traditional digital evaluation, with the aim of providing an objective evaluation of fetal head descent1−5. Despite an increasing number of studies on the subject, the application of this method in everyday clinical practice remains difficult, probably because of the technical difficulty in obtaining most of the sonographic parameters that have been suggested thus far6, 7. However, Eggebø et al. have proposed a measurement that is simply obtained, i.e. the distance between the fetal skull and the perineum on transperineal ultrasound (the head–perineum distance (HPD))3 (Figure 1a). More recently we have proposed another simple index of fetal head station inspired by the obstetric literature, i.e. the distance between the lower edge of the maternal symphysis pubis and the fetal skull, along the infrapubic line (the fetal head–symphysis distance (HSD)) (Figure 1b)8. We studied HSD with three-dimensional ultrasound which gave us the opportunity to measure both HPD and HSD retrospectively using the volume datasets we had stored (Figure 2). As shown in Figure 3, we found good correlation between the two measurements (Pearson's r coefficient, 0.826; P < 0.001), suggesting that it may be possible to use the two parameters interchangeably in assessment of fetal head station. Whether HPD or HSD is more useful in difficult clinical situations (e.g. prior to instrumental delivery) remains to be elucidated. We stress that we evaluated both parameters in sonographic volumes that had been acquired in the mid-sagittal plane, whereas HPD is classically evaluated in the axial plane. However, due to the clear definition given by Eggebø et al. of the HPD as ‘the shortest distance from the outer bony limit of the fetal skull to the skin surface of the perineum’3, we do not think that rotation of the ultrasound probe would result in any difference in the evaluation of this parameter. To summarize, both HPD and HSD are objective, simple and reliable indices of fetal station evaluation in labor and correlate highly with each other. We strongly encourage prospective studies on the use of these measurements. However, we feel that there is already sufficient evidence to justify their use as complementary parameters in the labor ward, especially in clinically challenging situations when the highly subjective digital evaluation remains the only tool in the armamentarium of obstetric personnel. A. Youssef*, F. Bellussi, E. Maroni, G. Pilu, N. Rizzo and T. Ghi Department of Obstetrics and Gynecology, Sant'Orsola-Malpighi University Hospital, University of Bologna, Via Massarenti, 40138 Bologna, Italy *Correspondence. (e-mail: [email protected])