Fetal Skull and Its Significant in Labor

8/18/2019 Fetal Skull and Its Significant in Labor

1/40

CONTENT 1:Pathophysiology and mechanism of labour

THE FETUS:FETAL SKULL AND ITSSIGNIFICANCE IN LABOUR

ROZIAH ARABIModule Coordinator

FFFM5024 MODULE 2: INTRAPARTUM ADVANCED DIPLOMA IN MIDWIFERY 2014/2015


2/40

LEARNING OUTCOMES

At the end of this topic, students will be able to:1. Describe the regions of the fetal skull2. Describe the bones that make up the vault of

the fetal skull3. Describe the sutures and fontanelles4. Describe the various diameters of the fetal

skull and their significance in labour


3/40

General description of the fetal skull

Ossified frommembranous tissue asearly as 8 th weeks in-uteroProtects the most vital

organ of the body

Composed of:1. The base

2. The face3. The vault


4/40

1. The baseComposed of hard bones firmly united that protects the vitalcentres in the brain during labour

2. The face A part of the skull below the supra-orbital ridges (glabella) to

the junction of chin and neckCompose to 14 rigid bones (ossified from cartilage)3. The vault

Region above an imaginary line drawn from the orbitalregion to the nape of the neckFormed by 7 pieces of bones which are incompletelyossified at birth

Separated by sutures and fontanelles allows the scull tomould and compress during birth


5/40

The bones

Vault are made up of :2 frontal bones2 parietal bones

2 temporal bones1 occipital bone


6/40

The two frontal bones

These bones form the foreheadThey are roughly square in shapeThey cover the frontal lobes of the brain


7/40

The two parietal bones

These bones lie behind the frontal bonesOn either side of the skullRoughly square in shape with a bonyeminence at the centre known as the parietaleminence (the centre of ossification)The largest of all bones

Cover the parietal lobesof the brain


8/40

THE OCCIPITAL BONE

Is a single piece of bone lying belowthe parietal bone at the back of theheadIs triangular shape with a small

eminence at its centre known as theOccipital ProtuberanceIt covers the occipital lobe of thebrain and cerebellumThe lower part forms the marginof the foramen magnum &articulateswith the 1 st cervical vertebrae


9/40

The two temporal bones

Form part of the side wallsLie below the parietal bones in front of theears


10/40

The sutures

Sutures are membranous junction between 2 bonesImportant because they allow the bones to overlapThus reducing the size of the fetal skull and facilitating

delivery


11/40

The sutures are:

1. Frontal sutureRuns between the frontalbones

2. Sagittal sutureLies between the 2pieces of parietal bones

3. Coronal sutureLike a crown runningacross the headLies between the frontaland the parietal bones

4. Lambdoidal sututreRuns obliquely betweenthe parietal and theoccipital bone


12/40

The fontanelles

Fontanelles are membraneous spaces where2 or more sutures meet~ membraneous junction of sutures

Out of 6 fontanelles in the fetal skull, only 2are important

1. Anterior fontanelle (in front of the vault)

2. Posterior fontanelle (at the back of the vault)


13/40

The fontanellesThe anterior fontanelle

Known as the Bregmalarge diamond shaped space

At the junction of 4 sutures; thefrontal, coronal and sagittal

About 3-4 cm in length

1.5-2 cm in breadthPulsation of cerebral vesselscan be felt through itIf this fontanelle is felt duringVE, means that the fetus iseither in OP position or face to

pubesClose when the childis 18 months old

The posterior fontanelle

Known as LambdaLies at the junction of thesagittal and labdoidalSmall and triangular in shape

If this fontanelle is felt duringVE, means that the fetus is inthe OA positionClose when the child is 6weeks


14/40

These fontanelles are important structures offetal skull as they denote the position of thefetal head


15/40

The regions of the fetal skull

Fetal skull is divided into the following regions:1. The occiput

Area below the lambdoidal sutures andthe posterior fontanelle

2. The vertex Area between the anterior and posteriorfontanelles and the parietal eminenceslaterally

3. The sinciput or browLies between the supra-orbital ridgesbelow and the anterior fontanelle andcoronal sutures above

4. The faceLies below the level of the supra-orbitalridges


16/40

The 4 regions

Is important because its often referred to inobstetrics

A midwife should remember these regions

Besides knowing the regions, the attitude ofthe fetal skull also a vital

Attitude means the relation of the fetal parts –

head, spine and limbs to each other in thiscase to fetal skull


17/40

ATTITUDEThe fetal head is capable of a wide range of movements:

1. Well FlexionThe head bends till its chin touches the chest

Vertex presentation2. Extension

The head bends backwards till it touches the spineFace presentation

3. Deflexion (militiary attitude)The head is neither flexed nor extended, straight head

Brow presentation

4. RotationCircular movement of the head for more than 180degress


18/40

DIAMETERS

The presenting diameters of the fetal skull areimportant because they are the distancewhich the birth canal must stretch to allow thehead to go through during deliveryThese distances are known as

“ the antero-po ster ior(AP) diam eters o f theengaging diameters”

The AP diameter varies with the degree offlexion or extension of the head


19/40

The variation of AP diameters according to the presentation ofthe fetus

Presentation Antero-posterior diameter (engaging diameter)

Length in cm

1. Vertex : Occipitoanterior position Sub-occipito bregmatic 9.5

1. Vertex : occipitoposterior position Occipito-frontal 11.5

1. Face Submento-bregmatic 9.5

1. Brow Mentor-vertical 13.5


20/40

Diagram showing the AP diameters of the fetal skull

KEYWORDS:Diameter LengthSOB = sub occipito b regmatic 9.5 cm

SOF = sub occipito f rontal 10.0 cm

OF = o ccipito f rontal 11.5 cm

MV = m ento vertical 13.5 cm

SMV = sub m ento vertical 11.5 cm

SMB = sub m ento bregmatic 9.5 cm


21/40

The descriptions

1. SOBSub-occipito bregmatic diameter runs from the pointbelow the occipital protuberance to the centre of thebregma in vertex presentationIt is the engaging diameter for vertex presentation

2. SOFSub-occipito frontal diameter runs from below theoccipital protuberance to the centre of the sinciput

3. OFOccipito-frontal diameter runs from the occipitalprotuberance to the glabella or root of the noseIt is the engaging diameter for occipito-posterior position(OP)


22/40

The descriptions

4. MVMento-vertical diameter runs from the tip of the chin tothe centre of the vertexThe longest diameter of the fetal skull

It is the engaging diameter for brow presentation5. SMV

Sub-mento vertical diameter runs from the junction of thechin and neck to the centre of the vertex

6. SMBSub-mento bregmatic diameter runs from the junction ofthe chin and neck to the bregmaIt is the engaging diameter for face presentation


23/40

CIRCUMFERENCE

The important of knowing about the cephaliccircumferences is because it will help inunderstanding why certain presentation of the

fetal head is more favorable then the others.


24/40

Other important diameters to belearn are:

1. BiparietalBiparietal diameter extendsbetween the two pairetaleminenceIt measures 9.5 cm

2. BitemporalBitemporal diameter runsbetween the two extremities ofthe coronal sutureIt measures 8.5 cm

The engaging diameters varies inlength, the shorter diameter aremore favourable for delivery of thefetal head


25/40

Presentation & Denominator

Presentation is the fetus part that presented at thebrim of pelvis or at the lower segment of the uterus

Denominator is the bone of the presenting part thatshows the fetal position

There are 5 types of presentation & its denominator:1. Vertex presentation – denominator is occiput2. Brow presentation – denominator is sinciput3. Face presentation – denominator is mentum4. Breech presentation – denominator is sacrum5. Shoulder presentation – denominator is

acromium process


26/40

There are 5 types of presentation & itsdenominator:

1. Vertex presentation –

denominator is occiput2. Brow presentation –

denominator is sinciput3. Face presentation –

denominator is mentum4. Breech presentation –

denominator is sacrum5. Shoulder presentation –

denominator is acromiumprocess


27/40

Vertex presentation

1. Well flexed headWhen the head is well flexed, the sub-occipito-bregmatic and the biparietal are the 2 diameters ofthe presenting circular area and the circumference is

29 cm2. Deflexed head

When the head is deflexed, it is erect as in themilitary attitude. The engaging diameters are:

i. Occipito-frontal –

11.5cmii. Biparietal 9.5cm (transversely)iii. Bitemporal 8.5cm (transversely)


28/40

Brow presentation

When partial extension occurs, the engagingdiameter is mento-vertical, which is 13.5cmThe circumference is 38cmSo the engaging diameter is longer, and thecircumference is also larger

Attitude of head circumference Shape ofcircumference

1. Well flexed 29 cm Round

2. Deflexed 34.5 cm Ovoid

3. Partial Eextension 38 cm Round


29/40


30/40


31/40

SIGNIFICANCE OF THE FETAL SKULL INLABOUR

We will discuss how the attitude of the fetalhead influences labour

1. Complete flexion

If the attitude of the fetal head is completeflexion

the presentation is vertex the position isoccipito-anterior,

the engaging diameter is the sub-occipito-bregmatic (9.5cm)the circumference is small and circular in shape


32/40

Significant to labour:

The girdle of contact between the fetal skulland the cervix is goodImagine that the cervix is around the fetal

skullThere is equal stimulation and the uterinecontraction will be good

With good uterine contractions, the motherwill have normal delivery


33/40

2. DeflexionIf the attitude of the fetal head is one ofdeflexion or deflexed

The presentation is still vertex but the positionwill be occipito-posterior The engaging diameter is the occipito-frontal(11.5cm)

The circumference is ovoid in shape


34/40

Significant to labour:

The girdle of contact between the fetal skull andthe cervix is not goodImagine that the cervix is also around the fetal

skullHowever the girdle of contact between the fetalskull and the cervix will not be goodThere is unequal stimulation and the uterinecontraction and the uterine contractions are notgood it will be irregular There will be delay in the engagement of the

fetal prolonged labour


35/40

3. Extension

If the attitude of the fetal head is oneof extension,

the presentation will be the faceThe engaging diameter is the

submento-bregmatic (9.5 cm)Same as the engaging diameter for awell flexed headHowever, the face is made up of rigidbones

Rigid bones do not mould like thebones of the vaultThis also may results in prolongedlabour


36/40

4. Partial extensionIf the attitude of the fetal head is one ofpartial extension

The presentation will be browThe engaging diameter is the mento-vertical(13.5 cm), which is very longLabour will be obstructed and caesareansection got to be done


37/40

Bear in mind!

Attitude Significance to delivery

1. Complete flexion

2. Deflexion

3. Extension

4. Partial Extension

Normal labour

Prolonged labour

Prolonged labour

Obstructed labour


38/40

Conclusion

Having a good knowledge about the fetalskull is very important as this will help

you to identify the presentation , theposition of the fetal head and the

diameter that is distending the vaginaso that you could conduct the delivery of

the baby with minimal trauma to themother and baby .


39/40

Keywords to remember!

1. Presentation2. Position3. Engaging diameter 4. Girdle of contact5. Stimulation6. Uterine contraction

7. Type of labour and delivery


40/40

That’s all.

THANK YOU VERY MUCH FOR YOURATTENTION

Documents

Fetal Skull and Its Significant in Labor