32. The Fetal skull for KEATS
Page 1: Title and Instructor
Title: The Fetal Skull
Instructor: Rebecca Daley, Lecturer in Midwifery Education at Florence Nightingale Faculty of Nursing, Midwifery & Palliative Care
Page 2: Learning Outcomes
Identify the key anatomical features of the fetal skull.
Explain the significance of fetal skull diameters in relation to the maternal pelvis.
Understand the functional adaptations of the fetal skull during labour.
Page 3: Preparation for Session
Core Learning Activity:
Watch the "The Fetal Skull" video (9 min) from Health E-Learning and Media Team (HELM).
Page 4: Introduction to the Fetal Skull
The cranium protects the brain.
Fetal skull bones are not fully ossified and can move independently.
This flexibility helps the fetus navigate the maternal pelvis during labour.
Ossification continues throughout childhood to allow for brain growth.
Page 5: Fetal Skull Bones
Components:
Vault
Face
Base
At term, facial and base bones are fused, limiting movement.
Vault composition:
2 Frontal bones
2 Parietal bones
2 Temporal bones
1 Occipital bone
Page 6: Fetal Skull Sutures
Vault bones connected by sutures (soft fibrous tissue) that allow movement:
Frontal suture (joins frontal bones)
Sagittal suture (joins parietal bones)
Coronal suture (joins frontal and parietal bones)
Lambdoidal suture (joins parietals to occipital bone)
Page 7: Fetal Skull Fontanelles
Fontanelles: junctions of sutures that allow overlapping.
Anterior Fontanelle (Bregma):
Diamond shape, 2-2.5cm wide x 2.5-3cm long.
Closes around 18 months.
Posterior Fontanelle (Lambda):
Triangular shape, closes 1-2 months post-birth.
Palpation helps identify fetal position.
Page 8: Significant Landmarks of the Fetal Skull
Landmarks:
Sinciput (forehead)
Mentum (chin)
Bregma (anterior fontanelle)
Lambda (posterior fontanelle)
Vertex (highest point)
Occiput (over occipital bone)
Glabella (bridge of nose)
Page 9: Diameters of Fetal Skull
Key Transverse Measurements:
Biparietal diameter: ~9.5cm
Bitemporal diameter: ~8cm
Key Longitudinal Measurements:
Suboccipital bregmatic: ~9.5cm
Suboccipital frontal: ~10cm
Occipital frontal: ~11.5cm
Mentovertical: ~13.5cm
Submentovertical: ~11cm
Submentobregmatic: ~9.5cm
Page 10: Presenting Diameters
Presentation types and corresponding diameters:
Well flexed (Vertex) - SOB ~9.5cm
Partially flexed (Occipito-posterior) - SOF ~10cm
Erect (Cephalic) - OF ~11.5cm
Partially extended (Brow) - MV ~13.5cm
Extended (Face) - SMB ~9.5cm
Page 11: Moulding
Moulding: overlapping of skull bones allowing for smaller presenting part dimensions (~1.5cm reduction).
Normal moulding usually resolves in a few days.
Excessive moulding may lead to complications, such as tentorial tears.
Page 12: Key Measurements
Suboccipitofrontal: 10 cm, optimal for vertex presentation.
Submentobregmatic: 9.5 cm for face presentation.
Mentovertical: 13.5 cm for brow presentation.
Occipitofrontal: 11.5 cm for occipitoposterior position.
Submentovertical: 11 cm when not fully extended, face presentation.
Suboccipitobregmatic: 9.5 cm, optimal for cervical dilation.
Page 13: Sutures and Fontanelles
Lambdoidal Suture: Enables occipital bone movement during labour.
Occipital Bone: Defines occiput area.
Posterior Fontanelle (Lambda): Key for assessing fetal position during vaginal examinations.
Vault: Compresses to facilitate delivery process.
Page 14: Consolidating your Learning
Post-Teaching Activities:
Read relevant sections from Rankin's "Physiology in Childbearing" (Pages 257-261).
Page 15: References
Coad et al. (2020), Anatomy and Physiology for Midwives.
Marshall & Raynor (2020), Myles Textbook for Midwives.
Rankin (2017), Physiology in Childbearing.
Wylie (2005), Essential Anatomy and Physiology in Maternity Care.
Page 16: Contact Information
Rebecca Daley
Email: beccy.daley@kcl.ac.uk
Institution: KING'S College London