The fetal skull

Question 1

Biparietal diameter of the fetal skull is …

Answer 1

9.5 cm

Question 2

Occipitofrontal diameter of the fetal skull is…

Answer 2

11.5 cm

Question 3

Submentovertical diameter of the fetal skull…

Answer 3

11 cm

Question 4

Suboccipitofrontal diameter of the fetal skull…

Answer 4

10 cm

Question 5

What are sutures & what are the different types?

Answer 5

Sutures (where fetal skull bones attach to each other) are composed of soft fibrous tissue
Allows movement and overlapping.

Frontal suture → joins the frontal bones
Sagittal suture → joins the two parietal bones
Lambdoidal suture → joins the parietal bone and the occipital bone together

Question 6

What is fontanelle & what are the different types?

Answer 6

Where three or more sutures meet, a fontanelle (soft fibrous tissue) is formed:
The bregma → located where the two fontanelle and the two parietal bones meet. Kite shaped
The lambda → located where the parietal bones meets the occipital bone

Question 7

List the significant landmarks

Answer 7

The sinciput: FOREHEAD
The mentum: CHIN
The bregma: ANTERIOR FONTANELLE
The lambda: POSTERIOR FONTANELLE
The vertex: THE HIGHEST POINT IF THE FETAL SKULL
The occiput: AREA OVER THE OCCIPITAL BONE
The glabella: THE BRIDGE OF THE NOSE

Question 8

What is the fetal skull made up of?

Answer 8

Fetal skull is made up of the vault, face and base
VAULT: frontal bone, parietal bone, temporal bone and the occipital bone
Central point of ossification can be identified on the vault and are called frontal bosses, parietal eminences and occipital protuberance.
The face and the base are already fused at term and so allow little movement.

Question 9

What is moulding?

Answer 9

Moulding- bones have the capacity to ride over one another

Why is there moulding?
The skull passes through the pelvis during delivery and it occurs as a normal adaptation to the small diameters of the maternal pelvis and at delivery the skull shape can look distorted.

Question 10

What are the types of fetal skull assessment?

Answer 10

Longitudinal measurement → five key parts. During delivery, the attitude (the degree of flexion of the fetal head with its body) of the fetal head determines which of the diameters is presenting

Transverse measurement → biparietal (between the parietal eminences measures an average of 9.5 cm) and bitemporal diameters.

Question 11

What is Caput succedaneum?

Answer 11

Is an oedematous swelling which forms on the presenting part of the fetal skull
Caused by prolonged pressure on the cervix as it dilates
This often occurs in labours where the head is in a posterior position in the pelvis
This disappears within 36-48 hours

Question 12

What is Cephalhaematoma?

Answer 12

Develops after birth
Caused by rupture of small blood vessels under the peristeum of the bone of the skull as a result of friction during delivery between the fetal head and maternal pelvis
Commonly occurs in cases of mild cephalopelvic disproportion or rapid deliveries where the fetus has little to accommodate to the diameters of the pelvis
Will disappear completely after 6 weeks