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Intrapartum Year 1 > Fetal skull and Pelvis > Flashcards

Fetal skull and Pelvis Flashcards

1
Q

What is the complex structure of the fetal skull comprised of?

A

29 irregular flat bones with 22 symmetrically paired; 8 form the cranium, 14 the face and 7 the base.

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2
Q

What structures make up the cranium?

A

Frontal X1, Parietal X2, sphenoid X2, temporal X2, occipital X1

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3
Q

What are the two key functions of the fetal skull?

A

-Protection of the brain which is subjected to pressure as it descends through the birth canal.
-An ability to change shape, adapting to the process of labour in response to uterine contractions and the size and shape of the pelvis.

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4
Q

Label the View from above image of the skull (A)

A

A-Occipital Protuberance
B-Posterior fontanelle
C-Parietal eminence
D-Anterior fontanelle
E-Frontal eminence or boss
F- Frontal bone
G-Parietal bone
H- Occipital bone
1-Sagittal suture
2-Coronal suture
3-Frontal suture

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5
Q

Label the two transverse diameters of the fetal skull (B)

A

A-Biparietal diameter (9.5cm)
B-Bitempora; diameter (8.2cm)

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6
Q

What is the transverse diameter: biparietal a measure of and what does it measure?

A

Diameter between 2 parietal eminences= 9.5cm

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7
Q

What is the transverse diameter: bitemporal a measure of and what does it measure?

A

The diameter between the 2 furthest points of the coronal suture at the temples.

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8
Q

What are the 6 longitudinal diameters of the fetal skull?

A

Sub-occipito-bregmatic
Sub-occipitofrontal
occipitofrontal
mento-vertical
sub-mento-vertical
sub-mento-bregmatic

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9
Q

What is the measurement and the meaning of the transverse diameter:
sub-occipito-bregmatic

A

9.5cm: Below the occipital protuberance to the centre of the bregma (anterior frontanelle)

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10
Q

What is the measurement and the meaning of the transverse diameter:
Sub-occipitofrontal

A

10cm:Below the occipital protuberance to the centre of the frontal suture

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11
Q

What is the measurement and the meaning of the transverse diameter: Occipitofrontal

A

11.5cm: Occipital protuberance to the glabella

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12
Q

What is the measurement and the meaning of the transverse diameter: mento-vertical

A

13.5cm: Point of chin to the highest point on the vertex

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13
Q

What is the measurement and the meaning of the transverse diameter: sub-mento-vertical

A

11.5cm: Point where the chin joins the neck to the highest point of the vertex.

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14
Q

What is the measurement and the meaning of the transverse diameter: Sub-mento-bregmatic

A

9.5cm: Point where the chin joins the neck to the bregma (anterior frontanelle)

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15
Q

What happens as the vertex descends into the maternal pelvis?

A

It will encounter resistance from the maternal pelvic floor muscles. This will cause the flexion of the fetal head onto the thorax.

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16
Q

What does the fetal head diameter depend on?

A

The degree of neck flexion.

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17
Q

What are the 4 types of neck flexion ?

A
  • vertex (well-flexed)
    -Vertex (deflexed head)
    -Brow
    -Face
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18
Q

What is the measurement of the position: Vertex (well-flexed head)

A

9.5cm

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19
Q

What is the measurement of the position: Vertex (deflexed head)

A

11.5cm

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20
Q

What is the measurement of the position: Brow

A

14cm

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21
Q

What is the measurement of the position: Face

A

9.5cm

22
Q

Describe the vertex presentation

A
  • well flexed head
    -presenting diameters are sub-occipito-bregmatic (9.5cm) and bi-parietal (9.5cm)
    -Therefore, the presenting area is circular, which is most favourable for dilating the cervix and birth of the head.
  • The diameter that distends the vaginal orifice is the sub-occipito (10cm)
23
Q

Describe the vertex presentation (for a deflexed head)

A

Presenting diameters are occipito-frontal (11.5cm) and biparietal (9.5cm)
The diameter that distends the vaginal orifice is the occipitofrontal (10cm)

24
Q

What does the degree of flexion in the fetal skull determine?

A

The presenting diameter of the fetal skull and will influence the progress of labour

25
Q

What is the purpose of the maternal pelvis?

A

To facilitate the movement of walking, running, bending, kneeling.
To transmit the weight of the body.
To protect the pelvic organ

26
Q

What are the 4 ‘types’ of pelvis?

A

Gynecoid (typical female)
Android (typical male)
Anthropoid (narrow)
Platypelloid (wide)

27
Q

How is the pelvic shape applied in labour?

A

The fetus’ head and shoulders align with the wider, transversal diameter f the canal entrance (inlet).
Progressing through the pelvis, the fetus needs to adapt to the changing shape of the canal, which tends to be sagittally deeper at its midpoint
It is often transversally larger again at the outlet.

28
Q

What is the false pelvis?

A

The upper part of the pelvis characterisedf by the ‘flared’ part of the iliac bones and lies above the pelvic brim

29
Q

What 3 regions are the true pelvis characterised of?

A

The pelvic brim
The pelvic cavity
The pelvic outlet

30
Q

What are the eight landmarks of the pelvic brim?

A

The sacral promontory
The sacral wing
The sacroiliac joint
The iliopectineal line
The iliopectineal eminence
The superior ramus of the pubic bone
The upper inner border of the pubic bone
The upper inner border of the symphisis pubis.

31
Q

What is the oblique diameter and what does this mean

A

Extends from the right sacroiliac joint to the elft iliopectineal eminence or from the left scroiliac joint to the right illiopectineal eminence
Diameters=12cm (3-5)

32
Q

What is the transverse diameter and what doe sit extend between?

A

The widest point of the iliopecinteal lines=13cm (4 and 4)

33
Q

What is the diameter of the sacrocotyloid and what does it meaan?

A

Extends from the scaral promontory to the iliopecineal eminence= 9-9.5cm. The bi-parietal diameter of the fetal skull may get lodged here when in an occipit posterior position (1-5)

34
Q

What is the curve of carus formed from?

A

The middle portion of the pelvis extending from the pelvic brim to the pelvic outlet.

35
Q

What is the anterior wall formed from?

A

By the symphysis pubis and the pubic bone

36
Q

What is the pelvic outlet formed from?

A

Diamond shaped
Formed by the lower edges of pevic bones and the sacrotuberous ligament

37
Q

What are the angles and planes of the pelvis?

A

A ‘plane’ describes the relationship between the pelvis and a horizontal surface
They are imaginary flat surfaces at the brim, cavity and outlet.
The fetus must navigate the planes and angles of the pelvis during normal labour and birth following the ‘curve of carus’

38
Q

What is the levator ani muscle?

A

The alrgest component of the pelvic floor. It is a broad muscular sheet that attaches to the bodies of the pubic bone anteriorely, ischial spines posteriorly and to a thickened fascia of the obturator internus muscle.

39
Q

What is descent in labour?

A

Process whereby the fetal head moves into the pelvis.

40
Q

When does engagement occur?

A

When the widest diameter of the presenting part enters the pelvis.
As the fetal head engages, the head move towards the pelvic brim in either the left or right occipito-transverse position

41
Q

When does flexion occur in labour?

A

At the beginning of labour, fetal head usually in natural flexion.
As labour progresses, the head meets the resistance of the pelvic floor muscles encouraging flexion
Fetal axis pressure through the occiput pushes this lower
The forehead is pushed upwards by the resistance of the soft parts and so complete flexion is obtained.

42
Q

How does internal rotation of the head occur?

A

-When the occiput meets the resistance of the pelvic floor is rotates 45 degress (to OA)
-The gutter shape of the pelvic floor aids the internal rotation forwards to allow the head to emerge in the anterior-posterior diameter of the pelvic outlet.
-During the movement of internal rotation, the head is slightly twisted because the shoulders do not rotate at the same time.

43
Q

When does crowning occur?

A

The head is crowned when is has emerged under the pubic arch and no longer recedes between contractions
The widest transverse diameter (the biparietal diameter) is born.

44
Q

When does extension occur?

A

Once the head is crowned, extension takes place to allow the bregma, forehead and chin to pass over the perineum

45
Q

When does restitution occur and why?

A

-When the head is born, it ‘rights’ itself with the shoulders
-Because during the movement of internal rotation the head became slightly twisted because the shoulders did not rotate at the same time
-The baby’s neck is untwisted by restitution.

46
Q

When and why is internal rotation of shoulders undergone?

A

The anterior shoulder undergoes an internal rotation to free itself from under the pubic arch-it does this by reaching the levator ani muscle first and then rotating anteriorly under the pubic arch.

47
Q

When does lateral flexion occur?

A

-The curve of the birth canal causes the trunk of he baby to flex sideways as it is born.
(-If mother semi-recumbent, the angle of inclination and uterine pressure exerted means anterior shoulder tends to be born first.
-If forward-leaning r on all fours, angle of inclination and gravity means posterior shoulder tends to be born first.)

48
Q

Label the false and true pelvis (c)

A

A-False pelvis
B-Inlet
C-True Pelvis

49
Q

Label the pelvis (d)

A

A-sacro-iliac joints
B-Ilium
C-Ischial spine
D-Ischium
E-Symphysis pubis
F-Pubis
G-coccyx
H-Sacrum

50
Q

Fill out the graph for pelvic measurements given in cm (e)

A

A-12cm
B-13cm
C-12cm
D-12cm
E-13cm
F-12cm

51
Q
A

Intrapartum Year 1 (15 decks)

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