Female Pelvis

Question 1

What four bones make up the pelvis?

Answer 1

Two innominate bones, form the walls of the pelvis
One sacrum
One coccyx

Question 2

What three bones make up the innominate bones?

Answer 2

Ilium
Ischium
Pubis

Question 3

Give detail about the ilium

Answer 3

Upper flattened portion of the innominate bone
Upper board forms iliac crest

Outer surface is rough, attachment for the gluteus muscles
Inner surface smooth, iliac fossa

Question 4

Give detail on the ischium

Answer 4

Smaller bone
Inferior portion of the innominate bones
Ischial tuberosities can be felt through the buttocks and bear weight of body when sitting
Inside of ischium is ischial spines, if especially prominent can influence space for birth

Question 5

Give detail on the pubis

Answer 5

Small bone at front of pelvis
Composed of two rami
Suprpubicnangke needs to be at least 90degrees to permit passage of fetus

Question 6

Give detail on the sacrum

Answer 6

Situated between two ilia and forms posterior wall of pelvis
Composed of five vertebra
Deep curve, if flattened can prevent descent of fetus

Question 7

Give detail on the coccyx

Answer 7

Small triangular shaped bone situated beneath and articulating with the sacrum
Composed of four fused vertebrae, evolutionary remnants of ancestral tail
Hinged with sacrum, moves back and forward during passage of fetus

Question 8

Outline the supporting structures of the pelvis

Answer 8

Sacroiliac ligaments run in front of and behind the sacroiliac joint
Pubic ligaments present both in front and behind the symphysis pubis
Sacrotuberous ligaments run from the ischial tuberosities to the sacrum
Sacrospinous ligaments run from the ischial spines to the sacrum

Question 9

What happens to pelvis ligaments and joints in pregnancy?

Answer 9

Relax due to an increase in hormones in body

Fractionally increases pelvic size which can be vitally important for successful birth

Question 10

What is the difference between the false and true pelvis?

Answer 10

False- above the iliopectineal line

True- below

Question 11

What is cephalopelvic disproportion?

Answer 11

Head of fetus may not engage in late pregnancy (normal for multiparous women)
Fetus may be too large
This is cpd
May be because fetus is larger than average and pelvis is smaller than average

Question 12

What does the true pelvis consist of?

Answer 12

Brim
Cavity
Outlet

Question 13

What is the gynaecoid pelvis?

Answer 13

Most common

Optimal shape and size to allow fetus to pass

Question 14

With knowledge of presentation, position and attitude of the fetus what should the midwife be able to determine?

Answer 14

Identify whether there is sufficient room for the passage of the fetus
Understand why the fetus rotates as it move through the pelvis
Predict any difficulties that may develop

Question 15

What are he average diameters of the brim?

Answer 15

Anterior-posterior- 11cm
Oblique- 12cm
Transverse - 13cm

Question 16

What are the average diameters of the cavity?

Answer 16

Anterior-posterior, oblique and transverse- 12cm

Question 17

What are the average diameters of the outlet?

Answer 17

Anterior-posterior- 13cm
Oblique- 12cm
Transverse- 11cm

Question 18

What other diameters are relevant to the passage of the fetal head through the pelvis?

Answer 18

Sacrocotyloid - 9cm

Diagonal conjugate- 12.5cm

Question 19

Discuss the pelvic inclination

Answer 19

Due to curvature of the spine the pelvis as a whole is inclined
An imaginary line drawn at right angles describes the path of the fetus as it passes through the pelvis- known as the curve of Carus

Question 20

Discuss the differences in pelvic shape

Answer 20

Gynaecoid
Platypelloid
Anthropoid
Android
Pelvic shape varies with different women
Nutritional and traumatic factors effect certain sections of the pelvis

Question 21

How does the pelvis change in pregnancy?

Answer 21

Progesterone and relaxin cause ligaments and muscles to relax slightly increasing diameters of the pelvis
Also gives rise to movements of joints- often why a lot of women complain of lower back pain and discomfort when walking

Question 22

Outline the mechanism of labour

Answer 22

Descent
Flexion (presenting diameter of 9.5cm
Internal rotation of head, occiput lead and rotates 1/8 of a circle anteriorly when head meets pelvic floor. Shoulders no longer in alignment
Crowning
Head is born by process of extension, face sweeps perineum
Restitution - twist in the neck correcting the earlier internal rotation
Internal rotation of shoulders - anterior shoulder lies underneath symphysis pubis, occurring at the same time is external rotation of head
Lateral flexion- anterior shoulder is born. Spine bends sideways through curved birth canal

Question 23

How does the pelvis change in the postnatal period?

Answer 23

Hormonal influences on the musculoskeletal system including the pelvis are rapidly removed once the placenta has been delivered
Ligaments tighten again