A primigravida at 41 weeks gestation is in active labor. During assessment, the nurse notes that the fetal head is at +1 station with the sagittal suture palpated in the left occiput anterior (LOA) position. The cervix is 6 cm dilated and 80% effaced. Which assessment finding would indicate that internal rotation of the fetal head has occurred?

To understand why the sagittal suture is palpated in the occiput anterior (OA) position after internal rotation, it is essential to review the biomechanics of fetal descent. The fetal head must navigate the maternal pelvis, which has an inlet that is widest transversely and a mid-cavity/outlet that is widest anteroposteriorly. To accommodate this change in pelvic shape, the fetal head engages in a transverse or oblique diameter and must rotate internally to align its sagittal suture with the anteroposterior diameter of the pelvis.

The initial assessment describes a fetus in the left occiput anterior (LOA) position at +1 station. In the LOA position, the fetal occiput is directed toward the mother's left anterior pelvis. The sagittal suture is palpated in the right oblique diameter of the pelvis. For a vaginal birth to occur, the fetal occiput must rotate toward the symphysis pubis, the most spacious part of the anterior pelvis. This rotation is the mechanism of internal rotation. When internal rotation is complete, the occiput has rotated from its initial oblique or transverse position to lie directly behind the symphysis pubis. At this point, the sagittal suture is no longer in an oblique diameter; it is now aligned in the anteroposterior diameter, which is clinically defined as the occiput anterior (OA) position.

• Option 1 (ROA position): A change from LOA to right occiput anterior (ROA) would represent a rotation of the fetal head in the opposite direction, toward the right anterior pelvis. This is not the typical mechanism of internal rotation for a fetus starting in the LOA position and would not signify completion of the normal rotational process toward the symphysis pubis. Research on intrapartum ultrasound highlights that managing abnormal rotation, such as persistent occiput posterior or transverse positions, is a clinical challenge, but the physiological goal of rotation from an anterior oblique position is to reach the direct OA position [1,3].


• Option 2 (Descent to +2 station): Descent from +1 to +2 station indicates fetal progress, but it is a separate cardinal movement. A fetus can descend without completing internal rotation, a situation often seen in persistent occiput transverse (OT) or posterior (OP) positions, which are associated with labor dystocia [3,4]. The question specifically asks for the finding that indicates internal rotation has occurred, not just descent.


• Option 3 (Cervical change): Progression of cervical dilation from 6 cm to 8 cm with complete effacement reflects maternal response to labor and fetal descent. While these are positive indicators of labor progress, they do not provide direct physical evidence of the fetal head's rotational movement. The fetal position is determined by palpating the fetal skull sutures and fontanelles, not by cervical exam findings.

The direct OA position is the most favorable for delivery because it presents the smallest fetal head diameters to the pelvic outlet. When the sagittal suture is palpated in the anteroposterior diameter, with the posterior fontanelle anterior, it confirms that the vertex is well-flexed and internal rotation is complete. Failure to achieve this rotation, resulting in a persistent OP or OT position, is a common malposition that can lead to prolonged labor, operative vaginal delivery, or cesarean section. Studies investigating maternal postures and midwifery interventions aim to promote this anterior rotation, underscoring its critical role in achieving a spontaneous vaginal birth [2,3]. Therefore, the direct palpation of the sagittal suture in the anteroposterior plane, the OA position, is the definitive clinical sign that internal rotation has been successfully accomplished.