This piece was written during my residency while I was rotating through obstetric anesthesia. At the time, I was trying to make it simple enough for “a dumb anesthesiologist” to understand. I present this to you now, with some assorted editorial comments and translations (in bold) of the more egregious bits of medical jargon.
Due to the proportionately small size of the female pelvic outlet compared to the term neonate, fetal passage is easiest in the well-known head-down, vertex presentation. Variations make labor and delivery more difficult for mother and baby, with increased risk for morbidity and mortality. Perinatal morbidity and mortality associated with abnormal presentations may be as high as 25%; however, when corrected for higher incidence of prematurity and congenital malformations, risk may be similar to cephalic birth. Breech is the most common malpresentation (the others are included for completeness).
Although abnormal fetal lie is seen in 3-4% labors, incidence is 25% before 32nd week. It is for this reason that external versions to correct fetal lie are usually attempted after 37 weeks. Conditions associated with abnormal presentation can be broadly categorized into maternal and fetal barriers to normal fetal head engagement into the maternal pelvis.
- Abnormal uterus
- Abnormal placentation
- Multiparous uterus not in normal vertical orientation secondary to abdominal muscle laxity
- Septate uterus, bicornuate uterus, uterine myoma.
- Abnormal passage: pelvic contraction (congenital or acquired).
- Malformations— especially such that decrease fetal tone, strength, or mobility.
- Trisomies, joint contractures, myotonic dystrophy
- Prematurity– a smaller fetus is more likely than a term fetus to be accommodated by the uterus in breech position.
Face presentation: Up to 60% of fetuses with face presentation are malformed. Anencephaly is present in approximately one third of cases, fetal goiter is also seen. Only half of cases are found before the 2nd stage of labor, the remainder are discovered at delivery. Prognosis depends on orientation of chin; 70-80% deliver vaginally; 12-30% require cesarean section. Manual attempts to reduce place both mother and fetus at risk and are usually unsuccessful. Internal version and breech extraction have been associated with up to 60% of fetal loss and are not recommended. May cause prolonged labor. May be associated with neonatal laryngeo/ tracheal edema requiring intubation.
Brow presentation: Cephalopelvic disproportion, great parity, and prematurity are associated with 60% of cases. Detection as in face presentation, where only half of cases are discovered before second stage. May spontaneously convert to vertex presentation (usually) or face. May cause prolonged labor. Fetal mouth may engage on vaginal wall and halt descent. Watch and wait– if cephalopelvic disproportion or fetal distress is present, urgent operative delivery may be indicated.
Compound presentation: That is, a limb protruding along with the presenting part. Again, half are not detected until 2nd stage. Most consistently associated with prematurity. May also occur after external version of a breech. Cord prolapse in 11-20% of cases (may be occult), and is the most frequent complication, with trauma to extremity next. Do not manipulate extremity, do not attempt external version, go directly to cesearian section if problems develop. May cause prolonged labor. May reslove spontaneously.
Cord prolapse: Just one more way your baby can suffocate. If the umbilical cord slips through the cervix (normally the baby’s head prevents this as it plugs things up nicely; so does the baby’s bottom in a frank breech*) it will be compressed and can asphyxiate the baby. If this is not caught in time, the baby can die or become brain-damaged. If cord prolapse does occur, the baby must be delivered by c-section immediately—20 feet to the OR immediately, not “I live near a hospital so we’ll call 911 if anything happens”. One of the scariest c-sections I did was as a resident with a cord prolapse; the OB resident came into the OR riding on the bed with her hand trying to hold the cord in. The attending was not there but there was no question of waiting; that baby was out and OK five minutes from when the patient got the OR. The only reason I got to the OR that fast was because I was sleeping in a room 10 feet from it; the bed went by with the OBs yelling “anesthesia to the OR for stat c-section!”. The only reason my attending didn’t get there in time is because their call rooms were 50 feet farther away.
Oh, yeah. “May be occult” translates to: no one might know about it unless your baby has decels (oh noes, not monitoring!) and the OB (nasty OBs with their interventions) does an internal exam. Which is how that OB came to be riding to the OR on the patient’s bed with her hand up the mom’s hoo-hah.
* NB: this is one reason why complete and incomplete breech are contraindications to vaginal delivery.
Persistent occiput posterior: This presentation is a more painful labor for the parturient, as the fetal occiput puts pressure on the maternal sacral nerves. Controversy exists as to whether relaxation of pelvic floor muscles prevents the normal rotation of the fetus to occiput anterior during descent in the maternal pelvis. There is an association between persistent occiput posterior and labor epidurals, but it is not clear whether more epidurals are placed in OP presentations secondary to the increased maternal discomfort or if the epidural itself is actually a causative factor. If position persists, maximal relaxation of the pelvic floor is useful for assisted delivery, but not necessary for vacuum delivery.
Since I originally wrote this, more evidence has come out absolving labor epidurals. Certainly, modern techniques use much more dilute concentrations of local anesthetics which would (in theory) make persistent OP much less likely than epidural techniques that were used, say, in my mother’s time (I happened to be persistent OP and turned at the last minute). Back when I was born, epidurals were usually dosed through the needle and high volumes of concentrated local anesthetics were used to maximize time between doses; today (and when I trained), placement of a catheter allows continuous infusion of smaller doses. Having had a large volume of concentrated local anesthetic epidurally for my version, I can definitely see the downside of that technique for labor—I couldn’t even pee—pushing (had I been in labor) was out of the question.
In sum: labor epidurals do not cause persistent OP.
Transverse/Oblique: Seen in 2%of pregnancies at 32 weeks, and 0.33% at term. In pregnancies with transverse lie after 37 wks– 83% of infants spontaneously converted to breech or vertex. Associated with 9% fetal mortality if diagnosis is made early versus 27% mortality if the diagnosis is delayed. Maternal mortality up to 10%. Incidence of cord prolapse twenty times that of normal presentation. Internal version and breech extraction has unacceptably high mortality in transverse/ oblique presentations. Vaginal birth may be possible with premature infants.
One of the posts I recently read on another site referred to the statement that “transverse lie is not an emergency”; I (and the obstetric-hospital complex that never sees normal labors) beg to differ.
Breech: Of breech presentations, frank breech in 60%, incomplete (footling) breech 30%, complete breech 10%.
If breech presentation is detected before labor, external version may be attempted, where the obstetrician through external maneuvers attempts to turn the fetus to a vertex presentation. Caesarian section was required in 37% of breech presentations after attempted version versus 65% of non-verted patients. Maternal epidural anesthesia may increase success rate, although there is a theoretical risk that injury to the uterus could be masked; there is no definitive evidence to confirm or dispel this allegation. Placement of an epidural does allow for rapid extension of blockade to achieve surgical conditions if fetal distress or maternal injury does occur during the version attempt. Tocolytics (drugs that relax the uterus) have also been used to try to increase the chance of successful version. Factors associated with failure: maternal obesity, oligohydramnios, deep pelvic engagement of fetus. May cause fetomaternal transfusion, uterine rupture, or placental abruption. Because of the risks to mother and baby, version should be attempted approximately at 37-38 weeks, to give the fetus adequate opportunity to spontaneously “vert”, and to ensure fetal viability if emergent delivery is required. Ultrasound and fetal monitoring should be used, and facilities (OR) and personnel (obstetrician, anesthesiologist, pediatrician) for immediate operative delivery must be present.
External version works sometimes. It did not work for me. It was uncomfortable, especially before the epidural was placed. Sort of like getting an “Indian rub” on your belly (at one point I had three OBs pressing on my belly). Placental abruption etc is pretty unusual, but being in the right place with the right monitoring keeps things safer even if it should occur. I would recommend a) an OB very experienced in this technique and b) the epidural. I don’t think I would have tolerated it for more than about 5 minutes without one.
Risks to mother and baby of vaginal delivery of breech fetus:
Risks to mom:
- cervical lacerations
- perineal injury
- retained placenta
- maternal bleeding
Overall, breech vaginal birth is a lower maternal risk than cesarean section.
Risks to baby:
- Head entrapment: In the normal process of delivery, the fetal head is slowly molded so as to ease its passage through the maternal pelvis. In a breech birth, this does not occur until the umbilicus is in the maternal pelvis. Even presuming adequate cervical dilation by the fetal pelvis and thighs, the non-molded head may still not pass easily through the birth canal. The lower uterine segment may even contract after the delivery of the lower body. This is a very bad time to have difficulty, as the cord is compressed against the fetus in the birth canal and the neonatal airway is not available. Because of their disproportionately large head, this situation of head entrapment is more common in the premature infant. Which is to say, the baby’s head can become stuck, and the baby can suffocate as they cannot breathe AND the cord is compressed.
- Intracranial hemorrhage: Premature infants in particular are at risk of intracranial hemorrhage with their disproportionately large heads, delicate membranes, and poor clotting ability. This risk may be reduced with partial forceps delivery. Increased risk of cord prolapse: 0.5% in vertex and frank breech, and 10% in incomplete/ complete breech.
Contraindications to vaginal delivery: Vaginal delivery is contraindicated in infants that are too small (1000-1500g), because of increased risk of head trauma. It is also contraindicated in cases of cephalopelvic disproportion (fetus >4000g or maternal pelvis “inadequate”). In infants whose heads are hyperextended in utero secondary to breech position, vaginal delivery carries an unacceptable risk of cervical spine trauma. Vaginal delivery is not attempted in complete or footling breech presentations, due to high risk of both cord prolapse and compound presentation. Using above criteria, 65-75% of breech presentations require operative delivery.
As an aside, the ambiguity between cervical relating to the neck and cervical relating to the cervix made it hard to write this. Many OB groups no longer do elective breech deliveries because of the risk to the baby; my OBs group doesn’t. Since my first baby was breech, there was no temptation to go for vaginal delivery in my untried pelvis as a “elderly prime”; I was just fine not having the option for elective breech delivery.
Methods of vaginal delivery:
What an obstetrician can do: spontaneous delivery, partial breech extraction/ assisted breech delivery (forceps assist from umbilicus on), total breech extraction. Placing traction on the protruding infant can cause cervical spine trauma.
(see what I mean about “cervical”?) Don’t pull on the infant, you can break its neck.
What the anesthesiologist can do: women delivering a breech infant may feel rectal pressure and the urge to push against an incompletely dilated cervix. This is undesirable as it may lead to trauma to the cervix and increased risk of head entrapment. Epidural analgesia is very useful to avoid premature maternal expulsive efforts, not to mention ensuring a relatively well-rested mother who is ready to push at full cervical dilation, and who has adequate perineal anesthesia for a forceps assist. Perineal relaxation/ analgesia is also desirable in the second stage to facilitate delivery of the head.
In some cases, successful delivery will require both lower uterine segment and perineal musculature relaxation. In the absence of significant fetal distress, redosing the epidural may achieve adequate relaxation of the perineum (somatic muscle), and nitroglycerin may be administered for uterine relaxation (smooth muscle).
Perineal refers to the muscles of the pelvis and vagina. Redosing an epidural can cause paralysis of these muscles (this ain’t no walking epidural) maximizing the chances for a vaginal delivery. If the cervix contracts after delivery of the fetal pelvis but before the delivery of the head, relaxation of the uterus can prevent head entrapment (a phrase that isn’t inherently scary but still scares me green).
As an aside, the scariest vaginal delivery I ever saw was an elective breech done in the OR. Fortunately, none of these maneuvers were necessary; however, we were in the room at all times just in case. I believe the mother did deliver on all fours.
If relaxation is inadequate, or fetal distress is present, rapid induction of general anesthesia may be necessary– profound somatatic relaxation of perineal muscle is achieved with succinylcholine, and relaxation of the lower uterine segment occurs secondary to halogenated agents and/or additional nitroglycerin. If all else fails, a c-section may be necessary to save the life of the baby. That was another reason we were all in the OR during the “pushing phase”.
A word on shoulder dystocia:
Presumed causes: during descent, the infant torso can’t rotate (tight vagina secondary to obese parturient, or big baby), or infant has no time to rotate (precipitous delivery). This causes the infant’s shoulder to be trapped under the maternal pubic bone. However, 50% of infants with shoulder dystocia have no risk factors.
This is important. Half of all shoulder dystocia cases are a complete surprise to everyone concerned. It is much better to be surprised somewhere where there is an OB and an anesthesiologist. As the TV says, “Don’t try this at home”.
Signs of shoulder dystocia are retraction of the infant’s head against the maternal perineum (turtle sign) and halt of further descent. An orderly sequence of actions to free the shoulder and continue delivery is necessary, as the umbilicus will be compressed against the fetal abdomen until the dystocia is relived and the infant delivered.
The baby’s head may be out but they cannot breathe as the chest is still compressed by the birth canal. The cord is compressed against the baby’s body so placental blood flow is inadequate.
Maneuvers may include:
McRobert’s manuever –flexing mom’s legs accompanied by suprapubic pressure
Wood’s screw maneuver
Delivery of posterior shoulder and arm
intentional fracture of the infant’s clavicle
Zavanelli’s manuever — put baby back and do caesarian section (last ditch effort and thus associated with high fetal morbidity and mortality)
Many hospitals have shoulder dystocia drills to ensure “an orderly sequence of actions”.
What the anesthesiolgist can do: Maximaze perineal muscle relaxation– this may require general anesthesia. Nitroglycerin and halogenated agents will facilitate Zavanelli’s maneuver.
This is in some way a “scared straight” for women wanting to give birth outside a hospital, but even more for women who want to birth in a hospital but are being convinced to do otherwise by well intentioned (and we all know about good intentions) friends, strangers on the internet/ TV, etc. My timely delivery of this piece was prompted by a thread about a woman who was breech but was being convinced by her friends to birth at home.
Most babies come into this world vertex-first with little or no complications. Some babies that do not fall into this group may be detected prenatally; some may not. In those cases, fetal monitoring may be necessary for early detection and treatment to save the life of the baby.