Anatomy of the Bony Pelvis in Relation to Labour

Question 1

What are the functions of the bony pelvis?

Answer 1

Support of upper body and transference of weight
Attachment of muscles and external genitalia
Protection of pelvic organs and passage for childbirth

Question 2

What does the bony pelvis consist of?

Answer 2

Both hip bones, sacrum and coccyx

Question 3

What makes up the pelvic inlet?

Answer 3

Sacral promontory, ilium, superior pubic ramus, pubic symphysis

Question 4

What makes up the pelvic outlet?

Answer 4

Pubic symphysis, ischiopubic ramus, ischial tuberosities, sacrotuberous ligaments, coccyx

Question 5

Where is the pelvic cavity located?

Answer 5

Lies within bony pelvis = continuous with abdominal cavity above, lies between pelvic inlet and pelvic floor

Question 6

What are the bony landmarks of the pelvis?

Answer 6

Anterior = ASIS, iliac crest
Posterior = PSIS, iliac crest

Question 7

Where does the sacrotuberous ligament attach?

Answer 7

The sacrum and ischial tuberosity

Question 8

Where does the sacrospinous ligament attach?

Answer 8

Sacrum and ischial spine

Question 9

What are the functions of the pelvic ligaments?

Answer 9

Protection against sudden weight transfer

Relax during later pregnancy

Question 10

What are the usual features of pelvic fractures?

Answer 10

Tend to be multiple or combined with joint dislocation

Question 11

What can pelvic trauma cause?

Answer 11

Life threatening haemorrhage and damage to pelvic organs

Question 12

What is moulding?

Answer 12

Movement of one bone over another to allow foetal head to pass through pelvis during labour

Question 13

What are the borders of the vertex of the foetal skull?

Answer 13

Outlined by anterior and posterior fontanelles and the two parietal eminences

Question 14

Why is the foetal head longer than it is wide?

Answer 14

The occipitofrontal eminence is longer than the biparietal diameter

Question 15

How do the diameters of the pelvic inlet relate to each other?

Answer 15

Transverse diameter of pelvis is wider than the AP diameter

Question 16

How should the foetus ideally enter the pelvic cavity?

Answer 16

Facing either left or right (transverse facing)

Question 17

What does the station refer to?

Answer 17

Distance of foetal head from the ischial spines

Question 18

What do the station numbers mean?

Answer 18

Negative number = head superior to spines

Positive number = head inferior to spines

Question 19

What should happen while the foetus is descending through the pelvic cavity?

Answer 19

The foetal head should rotate and be in a flexed position

Question 20

How do the diameters of the pelvic outlet relate to each other?

Answer 20

AP diameter is wider than the transverse diameter

Question 21

What position should the foetus ideally leave the pelvic cavity in?

Answer 21

In the occipito-anterior position

Question 22

What position should the foetal head be in during delivery?

Answer 22

Extension

Question 23

What happens once the baby’s head has been delivered?

Answer 23

There is further rotation so that the shoulders and the rest of the baby can then be delivered

Question 24

Where does the inguinal ligament attach?

Answer 24

Between ASIS and pubic tubercle

Question 25

What position are the ischial spines palpable at on vaginal examination?

Answer 25

At approximately 4 and 8 o’clock positions

Question 26

What are the differences between the male and female pelvises?

Answer 26

AP and transverse diameters of female pelvis are larger, both at the pelvic inlet and outlet
Suprapubic angle and pubic arch are wider in females
Pelvic cavity is more shallow in females

Question 27

What is the anterior fontanelle called once it closes?

Answer 27

The bregma

Question 28

When do the anterior and posterior fontanelles close?

Answer 28

Anterior = 18 months - 2 years 
Posterior = 6 months - 1 year