EP01.02: Correlation between the sonographic measurement of the occiput spine angle and the fetal head station in the 1st stage of labour

During active labour fetal head is subjected to progressive flexion during descent. It is possible to quantify the degree of fetal head flexion by measuring at suprapubic ultrasound the angle between the occiput and the cervical spine (Occipital Spine Angle o OSA). The aim of this study was to assess the correlation between the OSA and the fetal head station. A series of low risk pregnant women in the 1st stage of labour were prospectively included and submitted to suprapubic ultrasound. Among the fetuses with anterior or transverse occiput the angle formed the occipital bone and the cervical spine was measured (OSA angle). Cases with posterior occiput position were excluded. Clinical assessment of the fetal station was subsequently performed by a blinded examiner. The correlation between the width of the angle and the station was evaluated. Overall 117 patients with OA and OT fetal position were included in the study group. Among these the fetal station was clinically described at a −3, −2 e −1 cm from ischial spines respectively in 17 (14.5%), 79 (67.5%) e 21 (17.9%) cases. The OSA width seemed directly related to the fetal station showing significantly higher values the lower was fetal station (119.3° station −3 vs. 125.0° station −2 vs. 131.5° station −1; p value < 0.001). The OSA angle width shows significant differences in relation with fetal head station. This confirms that the degree of fetal head flexion is subjected to progressive increase during fetal head descent.