Similar to vertex delivery, spontaneous expulsion of a breech fetus entails sequential cardinal movements. First, engagement and descent of the breech usually take place with the bitrochanteric diameter in one of the oblique pelvic diameters. The anterior hip usually descends more rapidly than the posterior hip, and when the resistance of the pelvic Boor is met, internal rotation of 45 degrees usually follows, bringing the anterior hip toward the pubic arch and allowing the bitrochanteric diameter to occupy the anteroposterior diameter of the pelvic outlet. If the posterior extremity is prolapsed, however, it, rather than the anterior hip, rotates to the symphysis pubis.
After rotation, descent continues until the perineum is distended by the advancing breech, and the anterior hip appears at the vulva. By lateral lexion of the fetal body, the posterior hip then is forced over the perineum, which retracts over the fetal buttocks, thus allowing the fetus to straighten out when the anterior hip is born (Fig. 28-4). he legs and feet follow the breech and may be born spontaneously or require aid.
FIGURE 28-4 The hips of the frank breech are delivering over the perineum. The anterior hip usually delivers first.
After the birth of the breech, there is slight external rotation, with the back turning anteriorly as the shoulders are brought into relation with one of the oblique diameters of the pelvis. The shoulders then descend rapidly and undergo internal rotation, with the bisacromial diameter occupying the anteroposterior plane. Immediately following the shoulders, the head, which is normally sharply flexed on the thorax, enters the pelvis in one of the oblique diameters and then rotates to bring the posterior portion of the neck under the symphysis pubis. The head is then born in flexion.
The breech may engage in the transverse diameter of the pelvis, with the sacrum directed anteriorly or posteriorly. he mechanism oflabor in the transverse position difers only in that internal rotation is through an arc of 90 rather than 45 degrees. Infrequently, rotation renders the back of the fetus to lie posteriorly instead of anteriorly. Such rotation is prevented if possible. Although the head can be delivered by allowing the chin and face to pass beneath the symphysis, the slightest traction on the body may cause extension of the head, which increases the diameter of the head that must pass through the pelvis.
With breech delivery, successively larger and less compressible parts are born. Thus, spontaneous expulsion is the exception, and vaginal delivery typically requires skilled provider participation for the fetus to navigate the birth canal. Noteworthy clinical pearls are provided by Yeomans (2017) in the third edition of Cunningham and Gilstrap s Operative Obstetrics.
First, with all breech deliveries, unless the perineum is considerably lax, an episiotomy is made and is an important adjunct to delivery. As discussed in Chapter 27 (p. 529), mediolateral episiotomy may be preferred for its lower associated risk of anal
FIGURE 28-5 To deliver the left leg, two fingers of the provider's left hand are placed beneath and parallel to the femur. The thigh is then slightly abducted and pressure from the fingertips in the popliteal fossa should induce knee flexion and bring the foot within reach. The foot is then grasped to gently deliver the entire leg outside the vagina. A similar procedure is followed on the right. (Figures 28-5 though 28-8: Reproduced with permission from Yeomans ER: Vaginal breech delivery. In Yeomans ER, Hoffman BL, Gilstrap LC III, et al (eds): Cunningham and Gilstrap's Operative Obstetrics, 3rd ed. New (ork, McGraw-Hili Education, 201o7.)