2. LEARNINGOUTCOMES
❑Overview of the bony pelvis
❑Describe the structure and divisions of the
female pelvis
❑Explain the landmarks and measurements of
the bony pelvis
❑Describe the types of female pelvises and
their obstetrical significance (SDL)
❑Explain the functions and significance of the
female pelvis
3. INTRODUCTION
The female pelvis is a bony canal through which
fetus passes during birth
The pelvis is lined by fibro – cartilage made up of
4 bones and is held tightly by ligaments
Knowledge of the structure, shape and size of
the female pelvis is critical to the midwife in
order to competently assess the woman's
progress in labour and note deviations from
normal.
4. INTRO CTD
The midwife should be able to identify the
relationship between the position and
descent of the fetus and the relevant
landmarks of the pelvis
5. THE PELVICBONES
❑The pelvis is made up of four bones namely:
▪Two Innominate bones (nameless/hip
bones)
▪One sacrum
▪One coccyx
8. INNOMINATEBONE
Each innominatebone has a large cup shaped socket
on its surface called the acetabulum
On lower aspect of innominate bone are 2 curves; the
greater sciatic notch from posterior inferior iliac
spine up to the l spine
Size of the notch can be used in assessing overall
shape and size of pelvis
The lesser sciatic notch between I spines and I
tuberosity
11. THE ILIUM
Large flared outer part of the hip
Has a concave anterior surface called Iliac Fossa
The margin where the hip rests is called Iliac
Crest
At the front of the Iliac crest are prominences
called anterior superior and anterior inferior
Iliac Spines
12. THE ILIUM
At the back are prominences called
posterior superior and posterior inferior
Iliac Spines
It contributes to ²/₅ of the Acetabulum
NB: the acetabulum is a deep cup that
receives the head of femur
13. ISCHIUM
Strongest ( broader and thicker) bone which
lies under Ilium and below acetabulum.
L shaped bone
Ends in marked protuberance called Ischial
Tuberosity where the body rests when sitting
14. ISCHIUM
The Ischial Spines arise near the junction of
Ilium and Ischium - juts into pelvic cavity
forming the shortest pelvic diameter and
serves as reference point during labor to
evaluate fetal descent in the pelvic canal
The station (level of PP is estimated in relation
to the level of the I spines)
It contributes to ²/₅ of the Acetabulum
15. THE PUBIS
❑Commonly called pubic bone
❑Much smaller bone which forms the front
(anterior aspect) of pelvis
❑It has main body and two arm like structures
which protrude out. These are called rami
positioned on either side. They are referred as
superior and inferior ramus
❑It forms 1/5 of the acetabulum
16. THE PUBIS
The 2 pubic bones meet at symphysis pubis
and the 2 inferior rami form the pubic arch. (
suprapubic angle needs to be 900 to allow
baby to pass underneath during vaginal birth
The triangular shaped space enclosed by the
body of pubic bone, rami and ischium is
called Obturator Foramen.
It contributes to ¹⁄₅ of the Acetabulum
17. THE SACRUM
The sacrum is a wedge shaped bone formed
by the fusion of five vertebrae
Articulates with the lumbar vertebrae above.
On the anterior portion is a projection into
the pelvic cavity called Sacral Promontory.
This projection is an obstetric guide in
determining pelvic measurements.
Where it is too pronounced it can impede
fetal descent into pelvis
18. THE SACRUM
The anterior surface is concave and is referred
to as Hollow of the Sacrum.
Laterally it extends into wings or alae and it
has four pairs of holes–foramina for
innervations
The anterior surface of the sacrum is concave
and is a distinctive feature of a rounded pelvic
cavity through which fetus descends during
labour and child birth.
19. THE COCCYX
This is a triangular bone consisting of
four vertebrae which may or may not
be fused.
It articulates with the sacrum at the
sacrococcygeal joint.
During child birth it moves backwards
to help enlarge the outlet
20.
21. THE PELVICJOINTS
Four pelvic joints
One Symphysis Pubis
formed by heavy fibro-cartilage and
anterior and superior pubic ligaments.
Joins the two pubic bones.
Its mobility increases during pregnancy
and causes pain when walking.
22. THE PELVICJOINTS
Two Sacroiliac Joints
◦Strongest joints between the sacrum and
Ilium.
◦ Connects the spine to the pelvis
One Sacrococcygeal Joint
◦joins the coccyx to the sacrum.
◦Moves backward during labor thus
widening outlet.
23. PELVIC LIGAMENTS
1. Interpubic ligaments at Symphysis pubis
2. Sacroiliac ligaments
3. Sacrococcygeal ligaments
The above hold pelvic joints
4. The Sacrotuberous ligament: from the sacrum
to the Ischial tuberosity
5. The Sacrospinous Ligaments: from the sacrum
to the Ischial Spines
25. FALSEPELVIS
This is a portion above the pelvic brim
It is formed by the upper flared out
portions of the Iliac bones
It protects abdominal organs but has no
pelvic significance.
26. TRUE PELVIS
Refers to the bony canal that the fetus needs to
pass through during normal mechanism of
labour
Lies below the pelvic brim up to the outlet.
Has 3 divisions namely:
◦The pelvic brim
◦The pelvic cavity
◦The pelvic outlet
27. THE PELVICBRIM
Also called pelvic inlet is the upper boarder of the
true pelvis
Round except where the sacral promontory projects
Its has the following significant landmarks
1. Sacral promontory
2. Alae or wings of the sacrum
3. sacroiliac joints
28. THE PELVICBRIM
4. Ileopectineal line
5. Ileopectineal eminence (roughened area
where ramus meet ischium)
6. Superior ramus of the pubic bone
7. Upper inner boarder of pubic bone
8. Upper inner boarder of the symphysis pubis
29.
30. PELVIC DIAMETERS
The brim has 3 principal diameters;
◦The transverse diameter
◦The oblique diameter
◦Anteroposterior diameter
31. PELVIC DIAMETERS
THE PELVIC BRIM
1. The Anteroposterior diameters
From sacral promontory to the symphysis pubis.
There are three conjugate diameters:
Anatomical Conjugate/True Conjugate:
this is from the sacral promontory to the
upper boarder of the symphysis pubis and
measures 12 cm
32. Obstetrical conjugate: from the sacral
promontory to the posterior boarder 1.25cm
below the upper surface and measures 11cm.
This represents the available space for fetal
passage.
It is measured indirectly by the diagonal
conjugate
From this diagonal conjugate, the obstetrical
conjugate can be estimated fairly accurately
by subtracting 1.5 or 2cm
33. Diagonal conjugate: from sacral
promontory to lower boarder of the
symphysis pubis. Its measured on
pelvic assessment and should
measure 12-13cm (12.5cm on
average).
35. The True Conjugate = 11 cm
The Obstet. Conjugate = 10.5cm
The Diagonal Conjugate = 12 cm
36. PELVIC DIAMETERS
2. Oblique Diameters
There are two oblique diameters the left
and right
Arise from sacroiliac joint to ileopectineal
eminence of the opposite side.
The name depend on the sacroiliac joint it
arises.
They both measure 12cm
37. 3. Transverse diameter
This is from one ileopectineal line of one
side to the ileopectineal line of the
opposite side
It measures 13cm
40. THE CAVITY
Extends from the brim to the outlet.
Anterior wall formed by pubic bones and
symphysis pubis. Depth approximately 4cm .
Posterior wall formed by the curve of the
sacrum which is 12cm.
Circular in shape
its diameters are difficult to measure. All are
considered to be 12cm.
41. THE OUTLET
Lower boarder of true pelvis. It is kite or
diamond shaped. Can be described as
◦Anatomical outlet: bounded by the lower
borders of each bone at the Ischial tuberosity
and the sacrotuberous ligaments
◦Obstetrical outlet: includes the narrow
pelvic strait of the sacrococcygeal joint, the
two Ischial spines and the lower boarder of the
symphysis pubis
42. DIAMETERS OF THE OUTLET
1. Anteroposterior diameters
From the lower boarder of the symphysis pubis to the
sacrococcygeal joint -13cm
2. Oblique diameters
Between obturator foramen and sacrospinous ligaments
-12cm
3. Transverse diameters
Two transverse diameters
1. Between the two Ischial tuberosities - 11cm
2. Between the two Ischial spines -10-11cm
43. TYPESOF PELVIS
The Caldwell-Moloy classification of pelvises is
widely used and describes the female pelvises
as being
1. Gynaecoid pelvis
2. Android pelvis
3. Anthropoid pelvis
4. Platypleoid pelvis
44. ADEQUACYOF THEPELVISTO ACHIEVEVAGINAL
DELIVERY
The sacral promontory should only be tipped at
a diagonal conjugate of 13 cm or more so that
when 2 cm are subtracted (thickness of pubic
bone and tissues) the obstetric conjugatecan
safely be estimated to be 11 cm
When the sacral promontory is tipped, the
pelvic brim should feel round.
Ischial spines should just be palpable and not
prominent on both sides of the pelvis
45. ADEQUACYOF THE PELVIS TO ACHIEVE
VAGINALDELIVERY
Sacrospinous ligaments should be flexible and
accommodating two fingerbreadths this indicates a
good sized sciatic notch
Sub pubic angle should also admit 2 fingerbreadths
or 90 degrees indicating an adequate outlet
Intertuberous diameter accept 4 knuckles on pelvic
exam/ should measure 10 cm or more
46.
47.
48. GENERALFUNCTIONSOF THE PELVIS
The pelvis has two major function
To allow movement of the body – walking
and running
To form a relatively fixed axis of the birth
passage
49. SIGNIFICANCEOF THE FEMALEPELVIS
The size and shape of the pelvis has great
significance to the progress and outcome of labor
Landmarks of the pelvis are useful in determining
position and descent of fetus during pregnancy and
labor. The fetus is described in relation to the pelvis
Knowledge of the pelvis acts as a guide to the
midwife in detecting deviation from the normal and
decision
