Relating Delivery Details to Pathophysiology Shoulder dystocia results from heterogeneous processes that

Relating Delivery Details to Pathophysiology Shoulder dystocia results from heterogeneous processes that

produce the same clinical effect. Among impaired or dys-

functional births characterized by fetopelvic disproportion, there is a continuum of obstruction wherein delivery of the fetal trunk is impeded following completed (or near com- pleted) delivery of the fetal head. Whereas the most common definition of shoulder dystocia requires the presence of a bony impaction preventing spontaneous delivery of the fetal trunk, its pathogenesis derives from variable contributions of both size and positional incompatibilities between fetal shoulder and maternal pelvic dimensions. Some shoulder dystocia events are caused mainly by positional misalignment of only marginally incompatible shoulder and pelvic dimen- sions (usually of a normal-sized infant and normal-sized pel- vis). Others arise from a significant shoulder-to-pelvis size incompatibility necessarily producing a “tight fit” between either a large-for-gestational age infant (most common) and a normal-to-large pelvic cavity or a normal-sized infant and a reduced-capacity pelvis (least common).

In a normal delivery, a winding, forward-progressing mo- tion occurs as the head and body traverse the birth canal. It is this rotational-type motion that accomplishes delivery of the shoulders following emergence of the head through the in- troitus. This is effectively an anatomical requirement im- posed by the typical arrangement of the bony boundaries of the pelvic inlet, midpelvis, and pelvic outlet, which is akin to threads of a screw. Thus, just after delivery of the head, the shoulders often must come to lie in an oblique orientation relative to the maternal pelvis before they can to descend into the midpelvis and deliver through the pelvic outlet. Shoulder dystocia occurs when the shoulders retain the anteroposte- rior orientation they had assumed on the head’s initial entry (usually in occiput transverse position) into the pelvic inlet and are unable to (or have yet to) rotate spontaneously to occupy the oblique diameter of the pelvis. Subsequently, the shoulders fail to deliver from behind the maternal pubic sym- physis.

Positional misalignments resulting in shoulder dystocia may also be produced by incomplete entry to the hollow of the sacrum by the posterior shoulder as the head delivers. This may occur when there is a compound presentation with the posterior arm beneath the posterior shoulder, from rela- tive lordosis of the maternal lumbosacral spine or from a prominent sacral promontory impeding descent of the pos- terior shoulder. The anterior shoulder then “rides high” and impacts behind the pubic symphysis. Another cause is insuf- ficient time allotted to permit spontaneous shoulder rotation to the normal oblique orientation relative to the pelvis. This can occur following precipitous delivery of the head pro- duced either by increased compliance of pelvic tissues or else by instrumented deliveries. This can even occur simply by too-hasty application of traction to the head immediately on its emergence from the birth canal (eg, “to keep the momen- tum going”) without awaiting the next contraction. It is also noteworthy that shoulder dystocia is disproportionately more common among anomalous or stillborn fetuses, sug- gesting that physiologic negotiation of the pelvic inlet and outlet is indeed a dynamic process, facilitated by normal fetal

responsiveness. 16 It is likely that any of these antecedents to a given shoulder dystocia can lead to an “accidental” or dynam-

Table 2 Documentation Suggested after a Delivery Compli- cated by a Shoulder Dystocia That May Help with Manage- ment of a Subsequent Pregnancy

Second stage of labor details Duration Time spent pushing Time the head was on the perineum prior to initiating

traction Total head to body delivery time Details of any operative interventions Type (forceps or vacuum) Indications Station initiated Asynclitism (if present) Rotation of the head (if performed)

Anesthesia details Use of any prophylactic positioning or maneuvers Position of head and side of restitution (manual or

spontaneous) Timing and type of episiotomy with extensions How and when shoulder dystocia was recognized (eg,

turtle sign, with first attempt at traction) Maneuvers (eg, prophylactic McRoberts’) and traction prior to diagnosis Evidence for compound presentation Other procedures

Nuchal cord management Suctioning of oropharynx Meconium management

Personnel present Description of each maneuver performed Maneuver documentation

Type and sequence of maneuvers Who performed which maneuvers Traction direction and orientation of head and thorax Effectiveness of each maneuver Fetal response to each maneuver Final successful maneuver Timing of management choices Clear descriptions of right versus left shoulder and

anterior versus posterior shoulder (eg, which was initially anterior, which was manipulated directly, which delivered first)

Birth weight Apgar scores Arterial and venous cord gas Infant injury (if any) Maternal injury (if any)