Diagnosis.—The recognition of this presentation is most easily secured by external abdominal palpation in pregnancy, which may be reinforced during labor by the internal examination.
Fig. 62.—The breech. Left-sacro-posterior position. (Lenoir and Tarnier.)
Externally the palpating fingers at the pelvic brim will note the absence of the hard, round head, and feel a mass, softer, quite irregular in shape, and less defined than customary. Movements also may be appreciated that would be too far down in the uterus if the head was presenting.
Next the hard, spherical tumor of the head can be outlined somewhere in the fundus, and the heart tones, instead of being below the umbilicus will be on the same level or even higher.
Vaginally the cervix is not filled out, the presenting part does not come down, but after labor has begun the distinctive features of the breech gradually become more evident, as they are driven into the pelvis.
One or both feet, or the buttocks, may be recognized. The examining finger may possibly enter the anus and be stained with meconium or pinched by the sphincter, which differentiates this orifice from the mouth.
One after another the characteristic landmarks appear until the diagnosis can not be doubtful. As soon as the sacrum is found or the legs definitely placed, the position can be named.
Mechanism.—The hips always enter the inlet in one of the oblique diameters and the back is turned to the same part of the uterine wall as in the corresponding vertex positions.
The acts described in the mechanism for vertex deliveries show a somewhat different order. Descent is first, then comes internal anterior rotation, which brings the anterior hip under the symphysis and its delivery is quickly followed by the posterior hip, which rolls out over the perineum.