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The essential prerequisite for the successful performance of breech extraction lies in the complete dilatation of the cervix and the absence of any serious mechanical obstacle. It is true that in a certain number of cases extraction through an imperfectly dilated cervix is possible, but this is usually effected only at the cost of deep cervical tears.
—J. Whitridge Williams (1903)
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Near term, the fetus typically has spontaneously assumed a cephalic presentation. Conversely, if the fetal buttocks or legs enter the pelvis before the head, the presentation is breech. This fetal lie is more common remote from term, as earlier in pregnancy each fetal pole has similar bulk. At term, breech presentation persists in approximately 3 to 5 percent of singleton deliveries (Cammu, 2014; Lyons, 2015; Macharey, 2017).
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CLASSIFICATION OF BREECH PRESENTATIONS
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The categories of frank, complete, and incomplete breech presentations differ in their varying relations between the lower extremities and buttocks. With a frank breech, lower extremities are flexed at the hips and extended at the knees, and thus the feet lie close to the head (Fig. 28-1). With a complete breech, both hips are flexed, and one or both knees are also flexed (Fig. 28-2). With an incomplete breech, one or both hips are extended. As a result, one or both feet or knees lie below the breech, such that a foot or knee is lowermost in the birth canal (Fig. 28-3). A footling breech is an incomplete breech with one or both feet below the breech.
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Of term breech fetuses, the neck may be extremely hyperextended in perhaps 5 percent, and the term stargazing fetus is used (Cimmino, 1975). With these, fetal or uterine anomalies may be more prevalent and are sought if not previously identified (Phelan, 1983). With this hyperextension, vaginal delivery can result in injury to the cervical spinal cord. Thus, if identified at term, this is an indication for cesarean delivery (Westgren, 1981). That said, flexion itself may be implicated, as cases of spinal cord injury have been reported following uneventful cesarean delivery of such fetuses (Hernandez-Marti, 1984). With transverse lie and similar hyperextension of the fetal neck, the term flying fetus is applied.
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Understanding the clinical settings that predispose to breech presentation can aid early recognition. Other than early gestational age, risk factors include extremes of amnionic fluid volume, multifetal gestation, hydrocephaly, anencephaly, ...