occipitoanterior

Occipitoanterior (OA) describes a fetal head position during labor in which the occipital bone of the fetal skull is oriented toward the maternal anterior pelvis. This orientation typically means the fetal chin is tucked toward the chest, aiding flexion and facilitating descent through the birth canal. OA can be further specified as left occipitoanterior (LOA) or right occipitoanterior (ROA), depending on whether the occiput is directed toward the mother’s left or right side.

In most labors, the cephalic presentation rotates to occipitoanterior as labor progresses. The head usually rotates internally to align with the anterior pelvis before crowning. OA is considered the most favorable position for vaginal delivery because it generally allows for efficient flexion of the head and smoother progression through the birth canal. By contrast, occipitoposterior (OP) positions, where the occiput faces the maternal posterior pelvis, are more commonly associated with back labor and longer, more difficult labor, though many OP labors ultimately resolve with vaginal delivery.

Diagnosis and clinical relevance: The fetal position is assessed by clinical examination during labor, often described using LOA, ROA, or OA terminology, and can be corroborated by imaging if needed. OA is the preferred position for vaginal birth and is associated with shorter labor and lower risk of operative delivery compared with less favorable positions. However, fetal position can change during labor, and management is guided by the clinical course and obstetric considerations.