Malposition - Occipitoposterior Position

Malposition - Occipitoposterior Position

• Occipitoposterior (OP) position is a cephalic presentation with the fetal back directed posteriorly. It's a malposition, not a malpresentation.
• OP position is the most common fetal malposition, occurring in approximately 40% of cases during antenatal period and 20% at the onset of labor.
• Most fetuses (90%) spontaneously rotate to an anterior position before delivery.
• The overall rate of occipitoposterior deliveries is 5.5%, but this is nearly twice as high in nulliparous women (7.2%) compared to multiparous women (4%).
• This position is significant due to potential labor abnormalities that can lead to adverse maternal and neonatal outcomes, especially during operative vaginal or Cesarean births.
• Right occipitoposterior (ROP) is more common than left occipitoposterior (LOP) due to the sigmoid colon reducing the left oblique diameter and the slightly longer right oblique diameter than the left.

Objectives

• Definition
• Epidemiology
• Etiology
• Diagnosis
• Management
• Complications

Etiology

• Pelvic shape (anthropoid) is the most common factor (85%).
• Other causes (15%) include maternal kyphosis, placenta previa, pelvic tumors, pendulous abdomen, polyhydramnios, and multiple pregnancies.

Diagnosis (During Pregnancy)

• Inspection: Abdomen looks flattened below the umbilicus, lacking a normal fetal contour. A groove may be present below the umbilicus, which corresponds to the fetal neck.
• Fetal movements might be detected near the midline.

Diagnosis (During Labor)

• Vaginal examination: Identifies occiput direction and degree of deflexion.

Palpation (Obstetric Grips)

• Fundal grip: Feels fetal buttock, midline back.
• Umbilical grip: Midline back—difficult to palpate, edge is felt away.
• First pelvic grip: Head is smaller and recedes from the fingers, feeling the bitemporal diameter instead of biparietal. Head is often not engaged due to deflexion.
• Second pelvic grip: Feels deflexed head where occiput/sinciput are at the same level. May get engaged, but only in difficult cases can it be differentiated from frank breech.
• Combined grip: Used in difficult cases to differentiate a head from a frank breech.

Diagnosis (Other)

• Auscultation: Fetal heart sounds (FHS) are heard in the flank, away from the midline.
• Ultrasonography/Lateral view x-ray: Confirms diagnosis, especially in obese women.

Mechanism of Labor

• Normal mechanism (90%): Deflexion corrects, long anterior rotation occurs, and fetus is delivered normally.
• Abnormal mechanisms (10%): Include deep transverse arrest, persistent occipitoposterior, and direct occipitoposterior (face to pubis).

Mechanism of Labor of OP

• Normal mechanism (90%): Occiput rotates anteriorly 3/8 of a circle.
• Abnormal mechanisms (10%): Include incomplete forward rotation (deep transverse arrest), non-rotation (oblique posterior arrest), and malrotation (direct OP).

Good and Bad Omens (in OP)

• Good omens: Efficient uterine contractions, moderate head size, roominess of the pelvis, good pelvic floor, no premature rupture of membranes, anterior shoulder not far from midline.
• Bad omens: Weak uterine contractions, persistent deflexion, abnormalities in the shape of the pelvis, relaxed pelvic floor, and other issues like full bladder, PROM, etc.

Management of Labor (First Stage)

• Exclude contracted pelvis and cord prolapse.
• Correct inertia with oxytocin (unless contraindicated).
• Use analgesia (pethidine or epidural) for marked backache.
• Avoid premature rupture of membranes.

Management of Labor (Second Stage)

• Wait for 60-90 minutes.
• Monitor mother and fetus.
• Combat inertia with oxytocin (unless contraindicated).
• Long internal rotation (3/8 circle) in about 90% of cases, then delivery is completed normally.
• Direct occipitoposterior (face to pubis) occurs in about 6% of cases, spontaneously or with outlet forceps.
• Episiotomy if needed to prevent perineal laceration due to large occipito-frontal diameter.

Continuation (of Labor)

• Deep transverse arrest (1%): Vacuum extraction, manual rotation, forceps rotation, cesarean, craniotomy (if fetal death).
• Persistent occipitoposterior (3%): Same management options as deep transverse arrest.

Maternal and Fetal Complications

• Maternal: Exhaustion, obstructed labor complications, perineal lacerations, atonic postpartum hemorrhage, anesthetic/operative risks, venous thrombosis, embolism, rectovaginal fistula, puerperal sepsis.
• Fetal: Asphyxia, birth injury, cord prolapse, intracranial hemorrhage.