Obstetrics 12: Malpresentations and Malpositions: Breech, Occiput Posterior Portal
Breech presentation may be classified into:
- Frank (45% to 50%)—hips flexed and legs extended over anterior body surface
- Complete (10% to 15%)—hips and legs flexed
- Footling (35% to 45%)—foot or knee presenting
Incidence and Etiology: Breech presentation is more common in preterm fetuses. As term approaches, the incidence drops to 3% to 4% of singleton deliveries.
Factors, other than gestational age, that appear to predispose to breech presentation include multiparity and uterine relaxation, hydramnios, hydrocephaly, previous breech, tumors in the pelvis, multiple gestation, oligohydramnios, anencephaly, and uterine anomalies.
Diagnosis: Abdominal palpation and vaginal exam usually reveals the diagnosis. Confirmation is by imaging. Immediate confirmation is unnecessary if a breech is detected in the second trimester, but if breech presentation persists into the third trimester, obtain ultrasound confirmation.
Antenatal Version: Conversion of breech to vertex presentation has been undertaken to lower the incidence of breech presentations in labor. Version is usually attempted about the 36th week and is performed where there are emergency Cesarean section facilities. Tocolytic agents are used to aid in relaxation, the FHR is continuously monitored, and the procedure is performed with ultrasound guidance. If the mother is Rh-negative, administer RhoGAM prophylaxis following the procedure.
The success rate of external cephalic version varies greatly, dependent on many fetal and maternal factors as well as on the skill of the operator. However, when performed after 36 weeks, the gain in vertex presentations at delivery is about 30%. Complications include fetal bradycardia, fetomaternal bleed, unexplained fetal mortality, and possible maternal mortality due to amniotic fluid embolism.
Delivery Route: Due to the greater risk of cord prolapse and head entrapment, manage footling breeches with Cesarean delivery. Frank and most complete breeches are managed on a case-by-case basis. The final choice of birth route depends upon the physician's delivery room experience.
Guidelines for consideration of vaginal delivery of the frank or complete breech:
- Facilities: Capability of emergency cesarean delivery
- Physician: Experience in vaginal breech delivery
- Anesthesia: Personnel present for delivery
- Fetal Size: Optimal estimates weight < 4000 g but > 1500 g
- Head Position and Size: Exclusion of hyperextension and macrocephaly
- Pelvimetry: Radiation exposure may be reduced by using CT pelvimetry, which may provide useful information on the type of breech, presentation, presence or absence of a flexed fetal head, and accurate pelvis measurements. All measurements should be average or above. Note the shape. Platypelloid (A-P narrowing) and android (heart-shaped) pelvises are much less favorable for vaginal delivery.
Mechanisms of Labor and Delivery: There are fundamental differences between labor and delivery in cephalic and breech presentations. With a breech, successively larger and much less compressible parts of the fetus are born after the smaller and compressible legs and pelvis.
Labor is allowed to continue as long as there is progressive dilation, effacement, and descent. Allow labor to evolve spontaneously, even if slow, as long as FHR patterns are normal, until the umbilicus appears at the introitus. Rapid delivery or traction on the fetal body prior to the delivery of the umbilicus may increase the risk of developing nuchal arms or extension of the head. The insertion of an episiotomy is usually recommended for delivery.
The breech will usually deliver with the axis of the fetal hips in the AP plane with the sacrum either on the maternal right or left. The anterior hip descends to the introitus and then, with lateral flexion of the fetal body, the posterior hip delivers over the perineum. External rotation follows delivery of the breech, allowing the infant’s back to turn anteriorly.
Allow the delivery to proceed spontaneously until the umbilicus appears at the introitus. Gently pull down several inches of cord to prevent tension as the body delivers and to monitor the pulse by palpation. In the case where the delivery is a breech presentation (flexed hips and extended knees), deliver the legs by Pinard maneuver. This consists of rotating the breech in the oblique diameter and inserting two fingers up along the posterior thigh of the fetus to the knee. This will cause the knee to flex and allow the leg to be grasped and withdrawn. Rotating the breech in the opposite direction facilitates delivery of the other leg.
After the umbilicus appears, gentle downward traction at a 45-degree angle may be used to draw the infant further into the pelvis. While performing this traction, the operator’s fingers should grasp the fetal pelvis rather than the abdomen to reduce the risk of injury to the fetus’ abdominal organs. Delivery of the arms is accomplished by rotating the infant’s body to the oblique and inserting one finger over the shoulder and following the arm to the elbow. Apply pressure to the arm to flex the elbow across the infant’s chest and withdraw the forearm. Rotation in the opposite direction allows delivery of the opposite arm. If nuchal arm exists, the infant’s feet may be pulled upward and laterally over the mother’s groin in the direction of the infant’s ventral surface. This motion draws the posterior shoulder over the perineum and permits delivery of the posterior arm. The anterior arm may then be delivered by depressing the body of the fetus.
After the shoulders emerge, delivery of the head is facilitated with the help of one or more assistants. The head should be in the OA position. A common technique is the modified Mauriceau Smellie Veit (MSV) maneuver, designed to maintain the fetal head in a flexed position throughout the delivery. Place one hand on top of the fetus, with one finger inserted into the vagina to apply firm pressure on the baby’s occiput. Place another finger of the same hand on each fetal shoulder. The provider’s other hand is placed beneath the baby, and upward pressure is applied to the fetal maxilla. (The classic Mauriceau maneuver, which describes placing a finger in the fetal mouth to apply pressure on the maxilla, is no longer recommended due to the risk that the provider will apply traction on the mandible and dislocate the jaw.) During the MSV maneuver, supra-pubic downward pressure on the occiput of the fetal head by an assistant helps to maintain the flexion of the head and facilitate delivery. Another assistant may wrap the fetal trunk with a sling and raise the body of the baby through a large arc as the head is being delivered, ensuring that the body stays in a neutral position relative to the head (avoiding hyperextension of the neck).
As the head emerges (or immediately after complete delivery), an assistant can suction the mouth and nose. The delivery of the head is completed by further flexion with the fetus at this point in an almost vertical position. The fetus can be flipped over unto the mother’s abdomen at this point and the delivery finished. In the case of difficulty with the delivery, Piper forceps may be applied to facilitate delivery of the fetal head.
Occiput Posterior (OP): The OP labor and delivery is not remarkably different from that of the occiput anterior (OA). Check the progress of labor by following the rate of cervical dilatation and the descent of the fetal head through the birth canal.
Presented with the situation of the fetal head well down into the pelvis and a persistent occiput posterior (OP) position, the possibilities for vaginal delivery are:
- Spontaneous delivery in the OP position
- Forceps delivery in the OP position
- Manual rotation to the OA position and delivery
- Forceps rotation to the OA position and delivery
Spontaneous Delivery: If the pelvic outlet is roomy and the vaginal outlet and perineum are somewhat relaxed from previous vaginal delivery, rapid spontaneous delivery often occurs. The OP position places more strain on the perineum. The head is driven against the perineum with more force than in the OA position. The second stage of labor may be prolonged. A generous episiotomy is usually needed.
Forceps Delivery in Occiput Posterior: Usual indications for applications of forceps apply. Mere presence of an OP position does not, in itself, indicate the use of forceps. The operator must carefully ascertain position and station of the head and assure good perineal anesthesia. If the biparietal diameter is engaged, forceps are applied in the usual manner. An episiotomy is usually necessary.
The mechanisms of labor are somewhat different with an OP position: extension will not occur, and further flexion of the head is limited. Therefore, apply horizontal traction to the forceps until the top of the nose comes beneath the symphysis. Slow, upward motion then exposes the occiput. Follow by downward pressure to deliver the face. The vacuum extractor may not work as well, due to inability to apply adequate traction and a tendency to deflex the head.
Manual Rotation: The cervix must be fully dilated, the head must be low in the pelvis, and the pelvis must be adequate to allow this maneuver. The operator’s hand, with palmar surface upward next to the fetal head, is inserted into the vagina. Place the thumb and fingers about the level of the ears. The fetal head may be dislodged upward slightly. During a contraction, exert rotational pressure on the occipital suture line clockwise with the left hand or counter-clockwise with the right. If the rotation is successful, spontaneous delivery may occur or forceps may be needed.
Forceps Rotation: Only skilled and experienced operators should consider this approach; generally, cesarean section is the preferable alternative to forceps rotation.
Compared to the OA position, labor with OP position is prolonged on the average by 1 hour in parous women and 2 hours in nulliparous women. The perinatal mortality rate does not differ significantly from the OA position, and there is no significant difference in APGAR scores. Extensions of the episiotomy, however, may be increased. In those cases in which the vertex in the OP position fails to descend (with adequate contractions), true CPD probably exists, and cesarean section is indicated.
Reference
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Advanced Life Support in Obstetrics, 3rd ed. American Academy of Family Physicians, 1996.