- The most frequently described occurrence prior to a shoulder dystocia emergency is the turtle” sign during contractions, in which the vertex is seen at the introitus, but subsequently recedes after maternal expulsive efforts.
- Upon encountering a shoulder dystocia, immediately announce the condition, summon help, and alert the anesthesia department. The mother’s pelvic capacity and the estimated fetal weight help determine just how difficult resolving shoulder dystocia may be.
- Physicians should concentrate gentle, downward applied force at the shoulder girdle—either to rotate it or dislodge it directly.
- Do not apply fundal pressure, as it tends to further aggravate shoulder impaction.
Though not a common obstetric occurrence, shoulder dystocia has the potential to lead to significant fetal morbidity—including nerve plexus injury, clavicle or humerus fracture or dislocation, soft tissue injury to the face, and asphyxia of varying severity1—and even mortality. Additionally, injuries sustained by the mother in the course of delivery may have lifelong consequences. In an effort to reduce these adverse outcomes, here we describe the risk factors predisposing a patient to shoulder dystocia, review the condition’s mechanism, outline management protocols, and offer our techniques for carrying out a safe delivery.
How it happens
In a normal delivery, once the fetal head is expelled, external rotation—or “restitution”—realigns the head to its proper location in relation to the cervical spine. With the head perpendicular to the shoulder girdle, the shoulders enter the pelvis in an oblique diameter at the inlet. Maternal expulsive efforts cause the anterior shoulder to transit underneath the pubis.
When both rotation and expulsive processes during the pelvic phase of labor fail, however, shoulder dystocia results. While there are differing opinions as to what constitutes true shoulder dystocia,2 it is usually defined as any nonspontaneous birth requiring extensive traction and specific maneuvers to disimpact the infant’s shoulder girdle. Under these conditions, the reported prevalence of shoulder dystocia is 0.15% to 1.7% of all live births.3
Diagnosis of shoulder dystocia is made after the fetal head is delivered and is seen to tightly approximate the maternal perineum.
In general, if the shoulder girdle fails to achieve rotation into the oblique diameters available at the inlet, or if that diameter is inadequate due to fetal size or maternal pelvic shape, completing the delivery process becomes difficult.4
Identifying those at risk
There are a number of clues obstetricians may encounter in the antepartum and intrapartum stages of pregnancy that can indicate a potential shoulder dystocia case (TABLE 1). Still, while these associations are helpful, it’s important to evaluate each labor and delivery individually.5-10
Antepartum signs of possible shoulder dystocia
|EFW=estimated fetal weight|
As delivery progresses, clinicians must continually assess the labor curve. Progress of the station during the second stage should be greater than 1 cm/hr. Prolongation of this stage—defined as more than 2 hours in the nulliparous patient and 1 hour in the parous patient, with arrest of descent at station 3 cm or higher—signals possible shoulder dystocia, as does minor degrees of malpresentation, such as occiput transverse, occiput posterior, and the presence of asynclitism (TABLE 2). In addition, the presence of cranial moulding, a sign of potential cephalopelvic disproportion, indicates a potential traumatic birth.
The most frequently described occurrence prior to a shoulder dystocia emergency is the presence of the “turtle” sign during contractions—that is, the vertex is seen at the introitus, but subsequently recedes after maternal expulsive efforts. Diagnosis of shoulder dystocia is made after the fetal head is delivered and is seen to tightly approximate the maternal perineum.
Things to keep in mind during delivery
|SIGNS OF SHOULDER DYSTOCIA|
|SHOULDER DYSTOCIA IS NOT CAUSED BY|
Resolving the problem
The mother’s pelvic capacity and the estimated fetal weight (EFW) help determine just how difficult resolving this condition may be. An experienced examiner should therefore assess the maternal pelvis for signs of contraction or inadequacy. An ultrasound may be used to estimate fetal weight (these assessments may vary by 6% to 22% in the fetus at term), though manual techniques can be just as reliable. During this time, we recommend talking with the patient about her previous obstetric history. Since many of the pregnancies in question involve parous women, it’s helpful to inquire whether this baby is bigger than her last.