What is the most common head position of the fetus, especially as pregnancy advances towards term?

Most Common Fetal Head Position

The occiput anterior (OA) position is the most common fetal head position at term and delivery, though occiput posterior (OP) is frequently the predominant position throughout much of the active first stage of labor before rotating to OA as the head descends. 1

Position Distribution Throughout Labor

Early Active Phase

• Occiput posterior is the most frequent position during the active first stage of labor, occurring in approximately 52% of cases at initial examination in the active phase 1
• Most OP positions cluster at the 4 o'clock or 8 o'clock positions rather than directly posterior 1
• Occiput transverse positions account for approximately 28% of cases early in active labor 1
• Occiput anterior positions represent only about 19% at the beginning of active phase 1

Transition to Delivery Position

• The fetal head rotates to occiput anterior as it descends, with OA becoming the most frequent position only at full dilatation 1
• By full cervical dilatation, 66% of fetuses have rotated to OA position (53 of 80 examined) 1
• At head-perineum distance ≤30 mm, 75% of fetuses are in OA position 1
• When angle of progression reaches ≥125° (corresponding to station +1), 73% are in OA position 1

Final Delivery Position Statistics

Rotation Patterns to Delivery

• All fetuses initially in OA position (100%) deliver in OA position 1
• 77% of fetuses initially in OP position (40 of 52) ultimately rotate and deliver in OA position 1
• 93% of fetuses initially in occiput transverse position (26 of 28) rotate and deliver in OA position 1
• Some fetuses rotate >180° over the 6 o'clock position from OP or transverse to reach OA 1

Persistent Malposition at Delivery

• Persistent OP position at delivery occurs in only 1.8% to 6% of births, representing the most common malposition 2
• Persistent OP is associated with failure of rotation rather than malrotation 2
• Six of eight cesarean deliveries in one study had persistent OP position throughout active labor 1

Clinical Implications

Key Timing of Rotation

• Most fetal head rotation occurs in the late first stage and second stage of labor, not early in the active phase 1
• OP positions persist in >50% of cases throughout the first stage but convert to OA by full dilatation in most cases 1
• The transition point appears to be when the head descends below the midpelvic plane 1

Risk Factors for Persistent Malposition

• Deflexion of the fetal head significantly increases cesarean delivery risk in both OA (adjusted OR 5.37) and OP positions (adjusted OR 13.9) 3
• Deflexion is diagnosed in 21.2% of OA fetuses and 43.2% of OP/transverse fetuses at full dilatation 3
• Persistent OP is associated with nulliparity, low maternal stature, previous cesarean section, longer labor stages, and epidural analgesia 2

Common Pitfall

Do not assume that an OP position detected early in active labor represents a pathologic malposition requiring intervention—this is the most common position during early active labor and most will spontaneously rotate to OA as descent occurs 1. However, persistent OP at full dilatation with head descent below midpelvis warrants heightened vigilance for operative delivery 1, 2.