Sonographic diagnosis of lateral asynclitism: A new subtype of fetal head malposition as a main determinant of early labor arrest

We report on the sonographic appearance of a new type of fetal head malposition in labor that has not been previously described systematically. In some circumstances, the fetal lie is characterized by a lateral orientation of the head with respect to the trunk and, on suprapubic ultrasound, a transverse section of the fetal chest together with the facial profile can be seen on the same image. These sonographic findings were documented in five cases of first-stage labor arrest. This report illustrates how, in these circumstances, ultrasound might be helpful in clarifying the precise cause of obstructed labor.