Page 20 - 33Elctronic Book (3) Normal Labor

• It bisects the true conjugate and is slightly shorter than the

anatomical transverse diameter.

• Oblique diameters:

o Right oblique diameter =12 cm

• from the right sacroiliac joint to the left iliopectineal eminence.

o Left oblique diameter = 12 cm

• from the left sacroiliac joint to the right iliopectineal eminence.

o Sacro-cotyloid diameters = 9-9.5 cm
• from the promontory of the sacrum to the right and left iliopectineal

eminence, so the right diameter ends at the right eminence and vice
versa.

➢ The Pelvic Cavity:
The pelvic cavity is the curved bony canal between the pelvic inlet & the pelvic

outlet. The anterior wall is short & is formed by the symphysis pubis &pubic bone.
The posterior wall is formed by the sacrum &the coccyx. Laterally by the sides of
pelvis.

➢ The pelvic outlet:
The lower border of the pubic bones at the front, and the lower border of the
sacrum at the back form the pelvic outlet. The ischial spines point into this space on
both sides. Figure 4 shows the dimensions of the space that the fetus must pass through

as it emerges from the mother’s pelvis. As you look at Figure 4, imagine that you are
the birth attendant who is looking up the birth canal, waiting to see the fetal head
emerging.

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