2. OBJECTIVES
1. Describe the divisions of the fetal skull.
2. Describe the bones of the vault of the fetal skull.
3. Explain the significance of the fetal skull in obstetrics.
3. 3 MAIN DIVISIONS
• The fetal skull is made
up of 3 divisions namely,
vault, face and base.
• The vault is the upper
dome-shaped part of
the fetal skull which
extends above the face
in front to the base of
the skull posteriorly.
4. BONES OF THE VAULT
• The vault is the most
significant in relation
to labour because it
undergoes changes.
• The vault consists of;
2 frontal bones
2 parietal bones
1 occipital bone
2 temporal bones
5. • The bones are separated by sutures.
• Sutures are membranous spaces, strong fibrous tissue that hold the
fetal skull bones together.
• Places where these sutures meet are called fontanelles.
• Position of the sutures and fontanelles in relation to the different
areas of the pelvis indicate the position of the head.
6. FRONTAL BONES
• They are 2 in number forming the anterior part of the vault.
• They are large and roughly curved.
• Start from upper borders of orbit up to the coronal sutures and
bregma.
• Are separated in between by the frontal suture.
• Have ossification centers known as frontal eminences.
7. PARIETAL BONES
• They are 2 in number forming the middle part of the vault.
• They are the largest of the cranial bones and are roughly square in
shape.
• Anteriorly they are separated from frontal bones by the coronal
suture and bregma.
• Posteriorly they are separated from occipital bone by the lambdoidal
suture and the lambda.
• Centrally they are divided by the sagittal suture.
• The have ossification centers called parietal eminences.
8. OCCIPITAL BONE
• There is 1 occipital bone forming the posterior part of the vault.
• Roughly triangular in shape and covers occipital lobes of the brain
and celebellum.
• Starts from the lambdoidal suture in front to the nape of the neck
posteriorly.
• At the central part is the external occipital protuberance commonly
called the occiput.
9. TEMPORAL BONE
• They are 2 in number forming part of the sidewalls of the vault.
• They are separated from the parietal bones above by the temporal
suture.
11. CLINICAL SIGNIFICANCE OF SUTURES
• Sutures make moulding possible during vaginal delivery.
• Palpation of the sagittal suture during vaginal examination gives an
idea of the degree of internal rotation.
12. FONTANELLES
Bregma; Anterior
fontanelle closes between
13 to 24 months.
Lambda: Posterior
fontanelle which closes
between 6 to 8 weeks.
• Mastoid
fontanelle/posterolateral
fontanelle
• Sphenoid
fontanelle/anterolateral
fontanelle
13. CLINICAL SIGNIFICANCE OF FONTANELLES
• Palpation of the posterior fontanelle during vaginal examination
denotes position of the head.
• Palpation of the anterior fontanelle during vaginal examination will
denote the degree of flexion of the head.
• After birth, fontanelles are used to asses the condition of the baby.
• The fontanelles remain membraneous for some time after birth. This
helps to accommodate the marked growth of the brain in the early
years of child development.
14. FETAL SKULL LANDMARKS
• Submental area; area below the chin and extends to the angle where
the chin meets the neck.
• The mentum; the chin
• Nasion; the root of the nose.
• Glabella/orbital ridges; the elevated area between the orbit ridges.
• Sinciput/brow/forehead; the area between the anterior fontanelle
and the glabella.
• Anterior fontanelle/bregma; diamond shaped where sagittal, coronal
and frontal suture meet.
15. LANDMARKS CONT’
• Vertex/parietal eminences/bosses; the area between the fontanelles
and bounded laterally by the parietal eminences.
• Posterior fontanelle/lambda; triangular shaped, T shaped, Y shaped
space where lambdoidal and sagittal sutures meet.
• Occiput; the area behind and inferior to the posterior fontanelle and
lambdoidal sutures.
16. 4 REGIONS OF THE FETAL SKULL
1. Vertex; it is the presentation when head is well flexed.
2. Sinciput; it presents when the head is deflexed and leads to
prolonged and obstructed labour.
3. Occiput; it is the first part of the head to be delivered in a vertex
presentation, it escapes under the pubic arc.
4. Face; the part of the skull from below the orbital ridges to the chin
and mentum. It presents when the head is extended.
NB: knowledge of the regions helps a midwife to state precisely what
area of the skull is presenting over the lower uterine pole during
labour.
17.
18. DIAMETERS OF THE FETAL SKULL
• Are measurements of the specific areas of the fetal skull that lie over
the pelvic brim.
• They are divided into two;
1. Transverse diameters
2. Anteroposterior diameters
19. TRANSVERSE DIAMETERS
• There are two transverse diameters of the fetal skull.
1. The bi-parietal diameter 9.5cm which is measured between two
parietal eminences.
2. The bi-temporal diameter 8.2cm measured between the junctions
of coronal and temporal sutures on either side of the skull. Between
the temples.
20. ANTERO-POSTERIOR DIAMETERS
• There are six antero-posterior diameters of the fetal skull.
Sub occipital-bregmatic diameter: Extends from below the occiput
protuberance to the bregma. Measures 9.5cm and presents on the
pelvic brim when the head is well flexed.
Sub occipital-frontal diameter: Extends from under the occiput to
the center of the brow/sinciput. Measures 10cm and presents when
the head is deflexed.
Sub mento-bregmatic diameter: from the junction of the neck and
chin to the bregma. Measures 9.5cm and presents when the head is
fully extended.
21. AP DIAMETERS CONT’
occipito-frontal diameter: from occipital protuberance to the
glabella. Measures 11.5cm.
Sub mento-vertical diameter: measures from the angle of the chin
with the neck, to the highest point of the vertex (about midway
between the anterior and posterior fontanelles). Measures 11.5cm.
Mento-vertical diameter: measured from the tip of the
chin/mentum, to a point on the vertex which is just above the
posterior fontanelle. Measures 13.5cm and is the largest diameter of
the fetal skull.
22.
23. SIGNIFICANCE OF FETAL SKULL
• Helps the obstetric midwife to know favourable and unfavourable
diameters the fetus may present with in labour.
• Fetal skull is the largest, hardest and difficult part of the foetus to be
delivered, whether it comes first or last.
• It contains delicate structures such as brain, nerves and great blood
vessels which can be subjected to injury during difficult labour and
delivery.
• It has the capacity to mould, hence facilitates passage of the head
through the maternal pelvis.
24. SIGNIFANCE CONT’
• Knowledge of the landmarks and diameters of the fetal skull assist in
determining presentation, position, attitude of the fetus and the
relation of the fetal skull to the maternal pelvis. This helps to deliver
the baby safely with minimal injuries to the mother and baby.
• Helps to detect abnormal presentations and positions.
• Degree of moulding and caput on the fetal head helps in determining
the condition of the fetus during labour and delivery.
• Assist in determining the progress and outcome of labour and
delivery.
