6.1 Obstetric anatomy Flashcards
What is the true (obstretric) conjugate of the pelvic inlet and what is it’s approximate length?
sacral promontory to upper and inner border of pubic symphysis, 11cm
What is the diagonal conjugate of the pelvic innlet and what is it’s approximate length?
(12.5cm): estimate of the true conjugate during transvaginal exam (sacral promontory to lower border of pubic symphysis)
What is the transverse diameter of the pelvic innlet and what is it’s approximate length?
(13.5cm): between the furthest 2 points of iliopectineal line
What is the oblique diameter of the pelvic innlet and what is it’s approximate length?
(12.5cm): sacroiliac joint to opposite iliopectineal eminence
What is the anteroposterior diameter of the pelvic outlet and what is it’s approximate length?
(9 – 11.5cm): tip of coccyx to lowest part of pubic symphysis (variable due to the movement of the coccyx during labour)
What is the bispinous diameter of the pelvic outlet and what is it’s approximate length?
(10.5cm): between tips of ischial spines → not fixed distance
What is the bituberous diameter of the pelvic outlet and what is it’s approximate length?
(11cm): between ischial tuberosities
which axis is the pelvic inlet widest along?
transverse axis
which axis is the pelvic outlet widest along?
AP axis
gyanaecoid pelvis
- incidence
- inlet shape
- side wall
- ischial spines
- sacrum
- subpubic arch
- 50% classic
- rounded bean
- striaght
- average
- well curved
- wide
android pelvis
- incidence
- inlet shape
- side wall
- ischial spines
- sacrum
- subpubic arch
- <30%
- heart (triangular)
- convergent
- prominent
- straight
- narrow
anthropid pelvis
- incidence
- inlet shape
- side wall
- ischial spines
- sacrum
- subpubic arch
- 20%
- long and narrow, oval
- straight
- non prominent
- variable
- narrow
platypelloid pelvis
- incidence
- inlet shape
- side wall
- ischial spines
- sacrum
- subpubic arch
- 3%
- oval (wider transversely)
- straight or divergent
- non prominent
- posteriorly inclined, flat
- wide
What does the coronal suture separate?
frontal from parietal bones
What does the sagittal suture separate?
2 parietal bones
What does the lambdoid suture separate?
occipital from parietal bones
what is the anterior fontanelle?
Diamond-shaped junction of the sagittal and coronal sutures
what is the posterior fontanelle?
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)
what is the occiput region of the infant’s head?
Area behind posterior fontanelle
what is the vertex region of the infant’s head?
Between anterior and posterior fontanelles and between parietal eminences
what is the bregma region of the infant’s head?
Anterior fontanelle
what is the sinciput region of the infant’s head?
Area in front of anterior fontanelle (divided into brow and head):
• Brow: between anterior fontanelle and roof of nose
• Face: below roof of nose
what’s the diameter measured when baby’s head is in a well flexed vertex position?
Suboccipitobregmatic (9.5cm)
what’s the diameter measured when baby’s head is in a deflexed (less flexed) vertex position?
Occipitofrontal (11cm)
what’s the diameter measured when baby’s head is in a brow presentation?
Verticomental (13.5cm)
what’s the diameter measured when baby’s head is in a deflexed (less flexed) face presentation?
Submentobregmatic (9.5cm)
definition of gravida
Number of times a woman has been pregnant
definition of para
Number of times a woman has given birth to a foetus of ≥ 24 weeks
definition of nulliparous
A woman who has not given birth previously
definition of primiparous
A woman who has given birth once previously
definition of multiparous
A woman who has given birth previously more than once
definition of grand multi
A woman who has already delivered ≥ 5 foetuses of ≥ 24 weeks
definition of foetal lie
Relationship between the foetal spine and maternal spine
definition of presentation
Anatomical part of the foetus at the lower segment of the pelvis
definition of presenting part
Lowest part of the foetus palpable on vaginal examination
definition of malpresentation
Any presentation other than a cephalic presentation
definition of attitude
Relationship of the foetal head to its spine
definition of caput
Localised swelling which can occur on the foetal scalp due to pressure from the cervix or the pelvic inlet
definition of moulding
Ability of the foetal skull bones to be compressed to achieve a reduced diameter of the head (to pass through the pelvis more easily)
what does longitudinal foetal lie mean?
Parallel to maternal spine (vertex/cephalic, breech → opposite)
what does transverse foetal lie mean?
Perpendicular (shoulder presentation)
what does oblique foetal lie mean?
At an angle (may be vertex/cephalic presentation)
when baby’s head is at maximal flexion, what is the presentation called?
vertex presentation (9.5cm; smallest engaging diameter)
when baby’s head is at deflexed head, what is the presentation called?
Vertex presentation but in occipito-posterior position (11cm)
when baby’s head is at extension of 90 degrees, what is the presentation called?
Brow presentation (13.5cm; largest engaging diameter → more than the outlet diameter → deliver via Caesarean section)
when baby’s head is at full extension what is the presentation called?
Face presentation (9.5cm)
definition of engagement?
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
definition of station?
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
definition of crowning?
When the foetal head is at the introitus (and does not disappear between contractions) → usually station +3
what is the diameter when the patient had her head in vertex (flexed) position?
Suboccipito-bregmatic (9.5cm)
what is the diameter when the patient had her head in vertex (deflexed) position?
occipitofrontal (11.5cm)
what is the diameter when the patient had her head in browed (extended) position?
occipitomental (13cm)
what is the diameter when the patient had her head in face (fully extended position?
submentobregmatic (9.5cm)
what is foetal caput?
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
