Female pelvisFemale pelvis

Anatomical position of Anatomical position of pelvispelvis

Tilted forwards and downwardsASIS and pubic tubercle should be

in the same coronal plane. Hence the front of pubic symphysis

faces downwards

The shape and size of the bony pelvis are important factors determining the outcome of labor.

The pelvic inlet is the entrance to the true pelvis. The plane of the pelvic inlet is almost circular in a normal female (or gynaecoid pelvis) with a slightly greater transverse than anterior-posterior diameter.

an oblique plane joining the sacral promontorythe arcuate and pectineal lines and the upper margin of the symphysis pubisis called the pelvic brim(pelvic inlet,linea terminalis)This divides the pelvis into greater(false) and lesser(true) pelvis

Pelvic inletPelvic inlet

(major and minor pelvis)

Pelvic brim

Measurements of inlet Measurements of inlet (pelvimetry)(pelvimetry)

A-P diameter- about 11cm

Transverse diameter- about 13..5cm(across the middles of the pelvic brim)

Oblique diameter-12.5 cm(From iliopubic eminence to

opposite sacroiliac joint)

Pelvic cavityPelvic cavity The A-P diameter called the obstetric conjugate diameter is measured between the midpoint of the sacral promontory and the nearest point on the posterior surface of the pubic symphysis.

Pelvic outletPelvic outlet

The pelvic outlet is narrower than the inletThe pelvic outlet is narrower than the inlet The A-P diameterThe A-P diameter is measured from the is measured from the

lower margin of pubic symphysis to the tip lower margin of pubic symphysis to the tip of the coccyx of the coccyx (10cm)(10cm)

The transverse diameterThe transverse diameter is between the is between the two ischial tuberositiestwo ischial tuberosities(10cm)(10cm)

The interspinous diameterThe interspinous diameter is the shortest is the shortest diameter in the pelvisdiameter in the pelvis(9cm)(9cm)

It is not necessary to remember the diameters of the pelvis in millimeters (or whatever unit one may choose!).

outletoutlet

Pelvimetry in X-rayPelvimetry in X-ray

Types of pelvis

Android(male-like)

Anthropoid(ape-like)

Platypelloid(flat)

The Caldwell-Moloy (1933) classification

Gynaecoid

Ideal shape, with round to slightly oval (obstetrical inlet slightly less transverse) inletbest chances for normal vaginal delivery.

•Gynaecoid:

Note the shapes of the inlet

The typical female pelvis The typical female pelvis hashas

broader greater sciatic broader greater sciatic notchnotch

broader ala of sacrum broader ala of sacrum compared to the body of compared to the body of sacrumsacrum

broader pubic bone broader pubic bone compared to the acetabulumcompared to the acetabulum

wider sub pubic anglewider sub pubic angle

These four differences are easiest to remember! These four points illustrate how the female pelvis is wider, to serve as the birth canal. 1.The broad greater sciatic notch increases the anteroposterior dimension.2.The broad ala of sacrum increases the size of the inlet.3.The broader pubic bone does the same to the inlet and the middle of the cavity. 4.The wide sub pubic angle pushes the ischial tuberosities farther apart, increasing the transverse diameter of the outlet.

Also note that in the female pelvis the sacrum is thrust more backwards, increasing the A-P diameter of the outlet. There are many other 'differences', but these few are significant for us

M F

Which is the female pelvis? Give four reasons for it

The true (T), obstetrical (O), and diagonal (D) conjugate diameters are indicated.