6.1 Obstetric anatomy

Question 1

What is the true (obstretric) conjugate of the pelvic inlet and what is it’s approximate length?

Answer 1

sacral promontory to upper and inner border of pubic symphysis, 11cm

Question 2

What is the diagonal conjugate of the pelvic innlet and what is it’s approximate length?

Answer 2

(12.5cm): estimate of the true conjugate during transvaginal exam (sacral promontory to lower border of pubic symphysis)

Question 3

What is the transverse diameter of the pelvic innlet and what is it’s approximate length?

Answer 3

(13.5cm): between the furthest 2 points of iliopectineal line

Question 4

What is the oblique diameter of the pelvic innlet and what is it’s approximate length?

Answer 4

(12.5cm): sacroiliac joint to opposite iliopectineal eminence

Question 5

What is the anteroposterior diameter of the pelvic outlet and what is it’s approximate length?

Answer 5

(9 – 11.5cm): tip of coccyx to lowest part of pubic symphysis (variable due to the movement of the coccyx during labour)

Question 6

What is the bispinous diameter of the pelvic outlet and what is it’s approximate length?

Answer 6

(10.5cm): between tips of ischial spines → not fixed distance

Question 7

What is the bituberous diameter of the pelvic outlet and what is it’s approximate length?

Answer 7

(11cm): between ischial tuberosities

Question 8

which axis is the pelvic inlet widest along?

Answer 8

transverse axis

Question 9

which axis is the pelvic outlet widest along?

Answer 9

AP axis

Question 10

gyanaecoid pelvis

• incidence
• inlet shape
• side wall
• ischial spines
• sacrum
• subpubic arch

Answer 10

• 50% classic
• rounded bean
• striaght
• average
• well curved
• wide

Question 11

android pelvis

• incidence
• inlet shape
• side wall
• ischial spines
• sacrum
• subpubic arch

Answer 11

• <30%
• heart (triangular)
• convergent
• prominent
• straight
• narrow

Question 12

anthropid pelvis

• incidence
• inlet shape
• side wall
• ischial spines
• sacrum
• subpubic arch

Answer 12

• 20%
• long and narrow, oval
• straight
• non prominent
• variable
• narrow

Question 13

platypelloid pelvis

• incidence
• inlet shape
• side wall
• ischial spines
• sacrum
• subpubic arch

Answer 13

• 3%
• oval (wider transversely)
• straight or divergent
• non prominent
• posteriorly inclined, flat
• wide

Question 14

What does the coronal suture separate?

Answer 14

frontal from parietal bones

Question 15

What does the sagittal suture separate?

Answer 15

2 parietal bones

Question 16

What does the lambdoid suture separate?

Answer 16

occipital from parietal bones

Question 17

what is the anterior fontanelle?

Answer 17

Diamond-shaped junction of the sagittal and coronal sutures

Question 18

what is the posterior fontanelle?

Answer 18

Triangular-shaped junction of sagittal and lambdoid sutures
• Allows the occipital bone to be displaced under the 2 parietal bones during childbirth → moulding (reduces volume of foetal skull)

Question 19

what is the occiput region of the infant’s head?

Answer 19

Area behind posterior fontanelle

Question 20

what is the vertex region of the infant’s head?

Answer 20

Between anterior and posterior fontanelles and between parietal eminences

Question 21

what is the bregma region of the infant’s head?

Answer 21

Anterior fontanelle

Question 22

what is the sinciput region of the infant’s head?

Answer 22

Area in front of anterior fontanelle (divided into brow and head):
• Brow: between anterior fontanelle and roof of nose
• Face: below roof of nose

Question 23

what’s the diameter measured when baby’s head is in a well flexed vertex position?

Answer 23

Suboccipitobregmatic (9.5cm)

Question 24

what’s the diameter measured when baby’s head is in a deflexed (less flexed) vertex position?

Answer 24

Occipitofrontal (11cm)

Question 25

what’s the diameter measured when baby’s head is in a brow presentation?

Answer 25

Verticomental (13.5cm)

Question 26

what’s the diameter measured when baby’s head is in a deflexed (less flexed) face presentation?

Answer 26

Submentobregmatic (9.5cm)

Question 27

definition of gravida

Answer 27

Number of times a woman has been pregnant

Question 28

definition of para

Answer 28

Number of times a woman has given birth to a foetus of ≥ 24 weeks

Question 29

definition of nulliparous

Answer 29

A woman who has not given birth previously

Question 30

definition of primiparous

Answer 30

A woman who has given birth once previously

Question 31

definition of multiparous

Answer 31

A woman who has given birth previously more than once

Question 32

definition of grand multi

Answer 32

A woman who has already delivered ≥ 5 foetuses of ≥ 24 weeks

Question 33

definition of foetal lie

Answer 33

Relationship between the foetal spine and maternal spine

Question 34

definition of presentation

Answer 34

Anatomical part of the foetus at the lower segment of the pelvis

Question 35

definition of presenting part

Answer 35

Lowest part of the foetus palpable on vaginal examination

Question 36

definition of malpresentation

Answer 36

Any presentation other than a cephalic presentation

Question 37

definition of attitude

Answer 37

Relationship of the foetal head to its spine

Question 38

definition of caput

Answer 38

Localised swelling which can occur on the foetal scalp due to pressure from the cervix or the pelvic inlet

Question 39

definition of moulding

Answer 39

Ability of the foetal skull bones to be compressed to achieve a reduced diameter of the head (to pass through the pelvis more easily)

Question 40

what does longitudinal foetal lie mean?

Answer 40

Parallel to maternal spine (vertex/cephalic, breech → opposite)

Question 41

what does transverse foetal lie mean?

Answer 41

Perpendicular (shoulder presentation)

Question 42

what does oblique foetal lie mean?

Answer 42

At an angle (may be vertex/cephalic presentation)

Question 43

when baby’s head is at maximal flexion, what is the presentation called?

Answer 43

vertex presentation (9.5cm; smallest engaging diameter)

Question 44

when baby’s head is at deflexed head, what is the presentation called?

Answer 44

Vertex presentation but in occipito-posterior position (11cm)

Question 45

when baby’s head is at extension of 90 degrees, what is the presentation called?

Answer 45

Brow presentation (13.5cm; largest engaging diameter → more than the outlet diameter → deliver via Caesarean section)

Question 46

when baby’s head is at full extension what is the presentation called?

Answer 46

Face presentation (9.5cm)

Question 47

definition of engagement?

Answer 47

When the biparietal diameter (of vertex presentation; widest diameter of presenting part) has passed through the pelvic inlet:
• Useful to assess the progress of labour

Question 48

definition of station?

Answer 48

Relationship of the foetal presenting part to the imaginary line connecting the 2 ischial spines (station 0):
• -3 to +3 refer to the number of cm above/below the line

Question 49

definition of crowning?

Answer 49

When the foetal head is at the introitus (and does not disappear between contractions) → usually station +3

Question 50

what is the diameter when the patient had her head in vertex (flexed) position?

Answer 50

Suboccipito-bregmatic (9.5cm)

Question 51

what is the diameter when the patient had her head in vertex (deflexed) position?

Answer 51

occipitofrontal (11.5cm)

Question 52

what is the diameter when the patient had her head in browed (extended) position?

Answer 52

occipitomental (13cm)

Question 53

what is the diameter when the patient had her head in face (fully extended position?

Answer 53

submentobregmatic (9.5cm)

Question 54

what is foetal caput?

Answer 54

localised swelling on the foetal scalp due to pressure placed on it by the cervix/pelvic inlet
• Collection of fluid between the scalp and periosteum
• Resolves spontaneously with no long-term effects