2D trans abdominal ultrasound was done during the first stage of labor. If fetal position is occiput anterior and fetal presentation is vertex, two dimensional sagittal picture of the fetal head and upper spine was acquired and stored in the ultrasound machine. On this image, the offline measurement of the angle formed by a line tangential to the occipital bone and a line tangential to the first vertebral body of the cervical spine (occiput-spine angle) will be performed to quantify the degree of fetal head flexion in respect to the trunk.