Obstetrical pelvic measurements which are important to know.

1. Obstetrical
pelvic
measurements

2. • The transverse diameter of the outlet is assessed
clinically by measuring the distance between the
ischial tuberosities along a plane passing across the
anus;
• The anteroposterior outlet diameter is measured
from the pubis to the sacrococcygeal joint.
• The most useful measurement clinically is, however,
the diagonal conjugate—from the lower border of
the pubic symphysis to the promontory of the
sacrum.

3. (a) The inlet,
(b) the outlet.
The measurements of
the female pelvis.

4. Transverse diameter AP diameter
Inlet 13 cm 11 cm
Mid pelvis 12 cm 12 cm
Outlet 11 cm 13 cm

5. (c) Lateral view to show the
diagonal conjugate.

6. • Another useful clinical guide is the subpubic arch:
the examiner’s four knuckles (i.e. his clenched fist)
should rest comfortably between the ischial
tuberosities below the pubic symphysis.
• Note that these measurements are all of the bony
pelvis; the ‘dynamic pelvis’ of the birth-canal, in fact,
is narrowed by the pelvic musculature, the rectum
and the thickness of the uterine wall. Today accurate
imaging techniques enable exact measurements to
be made of the bony pelvis.

7. • 1 The normal and its variants
• (a) Gynaecoid—normal.
• (b) Android—the masculine type of pelvis.
• (c) Platypelloid—shortened in the anteroposterior
diameter, increased in the transverse diameter (the
‘non-rachitic flat pelvis’).
• (d) Anthropoid—resembling that of an anthropoid
ape with a much lengthened anteroposterior and a
shortened transverse diameter.
Variations of the
pelvic shape

8. Pelvic variations
and abnormalities—
shown as diagrammatic
outlines of the pelvic
inlet.

9. • 2◊◊Symmetrically contracted pelvis
• That of a small woman but with a symmetrical shape.
• 3◊◊The Rachitic flat pelvis
• The sacrum is rotated so that the sacral promontory projects
forward and the coccyx tips backwards. The anteroposterior
diameter of the inlet is therefore narrowed, but that of the outlet is
increased. This deformity is typical of rickets, the result of vitamin D
deficiency.
• 4◊◊The asymmetrical
• Asymmetry can be due to a variety of causes such as
scoliosis, longstanding hip disease (e.g. congenital
dislocation), poliomyelitis, pelvic frac ture, congenital abnormality
due to thalidomide and the Naegele pelvis which is due to the
congenital absence of one wing of the sacrum or its destruction by
disease.