D efinir Oportunidades
3.14. SIX SIGMA y otros marcos GESTIÓN
3.14.4. Six Sigma y Lean Manufacturing
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UNIT 3 THE FETAL SKULL
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THE FETAL SKULL
Figure 18: Fetal Skull Thresyamma C.P. (2002)
3.0 MAIN CONTENT
3.1 The External Structures of the Fetal Skull
Fetal skull bones (Vault)The skull bones encase and protect the brain, which is very delicate and subjected to pressure when the fetal head passes down the birth canal.
Correct presentation of the smallest diameter of the fetal skull to the largest diameter of the mother’s bony pelvis is essential if delivery is to proceed normally. But if the presenting diameter of the fetal skull is larger than the maternal pelvic diameter, it needs very close attention for the baby to go through a normal vaginal delivery.
The fetal skull bones are as follows:
• The frontal bone, which forms the forehead. In the fetus, the frontal bone is in two halves, which fuse (join) into a single bone after the age of eight years.
• The two parietal bones, which lie on either side of the skull and occupy most of the skull.
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• The occipital bone, which forms the back of the skull and part of its base. It joins with the cervical vertebrae (neck bones in the spinal column, or backbone).
• The two temporal bones, one on each side of the head, closest to the ear.
The face: This area extends from the orbital ridge to the junction of the neck with the chin. It is composed of 14 fused bones.
The base: These bones are also firmly united and help to protect the brain.
Figure 18. Regions and landmarks in the fetal skull facing to the left, as seen from above.
Sutures: are joints between the bones of the skull. In the fetus they can
‘give’ a little under the pressure on the baby’s head as it passes down the birth canal. During early childhood, these sutures harden and the skull bones can no longer move relative to one another, as they can to a small extent in the fetus and newborn.
• The lambdoid suture forms the junction between the occipital and the frontal bone.
• The sagittal suture joins the two parietal bones together.
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• The coronal suture joins the frontal bone to the two parietal bones.
• The frontal suture joins the two frontal bones together.
Others are the sutures that separate the parietal bones from the temporal bones.
The Fontanelles: Fontanelles are formed where two or more sutures meet between the bones. There are 6 sutures on the vault but only two are of importance. These are:
1. Anterior Fontanelle (or bregma): Formed at the junction of the Sagittal, Fontal, and coronal sutures. It is a diamond-shaped membranous space. It has four angles which correspond with the entry of each suture. It is about 3-4cm long and 1.5cm wide. It is a valuable aid in vaginal examination to determining the position.
Cerebral pulsation can be felt through it and it is a guide to baby’s health – It bulges in brain infection or increase pressure and depressed in dehydration. Closes 18-24months after birth.
2. The Posterior fontanell – (lambda): Formed at the junction of the sagittal and lambdoidal sutures. It is a small triangular membranous space. It is felt on vaginal examination during labour in a well flexed head. It closes at 6 weeks after birth.
Regions and landmarks in the fetal skull
Figures 17 and 18 allow you to identify certain regions and landmarks in the fetal skull, which have particular importance for obstetric care because they may form the so-called presenting part of the fetus — that is, the part leading the way down the birth canal.
• The vertex is the area midway between the anterior fontanel, the two parietal bones and the posterior fontanel. A vertex presentation occurs when this part of the fetal skull is leading the way. This is the normal and the safest presentation for a vaginal delivery.
• The brow is the area of skull which extends from the anterior fontanel to the upper border of the eye. A brow presentation is a significant risk for the mother and the baby.
• The face extends from the upper ridge of the eye to the nose and chin (lower jaw). A face presentation is also a significant risk for the mother and baby.
• The occiput is the area between the base of the skull and the posterior fontanel. It is unusual and very risky for the occiput to be the presenting part.
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Other regions are:
• Glabella – is the bridge of the nose, between the eyebrows.
• Bregma – anterior fontanelle
• Lambda – Posterior fontanelle
• Mentum – Chin
Measurements of the fetal skull- Diameter of the fetal skull
These are the diameter the birth canal must stretch to allow the head to pass during labour. The largest being mento vertical 13.5cm.
1. Sub-Occipito Bregmatic (9.5cm) 2. Sub-Occipito Frontal (10cm) 3. Occipito Frontal (11.5m) 4. Mento Vertical (13.5cm) 5. Sub Mento Vertical(11.5) 6. Sub-mento Bregmatic (9.5cm) 7. Biparieta (9.5cm)
8. Bitemporal (8.2cm).
Circumferences
1. Sub-ocicpito bregmatic: is measurement taken round the occipital protuberance, parietal eminences and the bregma. Itis the circumference which passes through the pelvis in a well flexed head 33cm.
2. Occipito Frontal: It is measured through posterior fontanel, parietal eminence and the orbital ridge. It is found in an erect head-military attitude 33-36 cm.
3. Sub-occipito frontal: It is taken round the perimeter of suboccipito frontal 35cm.
4. Mento vertical: It is measured round the chin up to the vertex. It is found in partly extended head (Brow). It is the largest diameter of the fetal skull 38 cm.
Attitude of the head
This determines diameter that pass through the pelvis.
1. Vertex Presentation: A well flexed head. It is the most favourable. engaging diameters are sub-occipito bregmatic of 9.5cm, biparieta 9.5 cm and the circumference entering the brim is sub-occipito bregmatic 33cm.
2. Military attitude – deflexed head. The head is more erect.
Engaging diameters are occipito frontal 11.5cm Biparietal 9.5cm bitemporal 8.2cm. and circumference occipito frontal 35cm.
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3. Face Presentation: Extended head. The head is completely extended. The engaging diameter is sub-mento bregmatic 9.5cm, Bitemporal 8.2cm. sub-mento vertical of 11.5cm will descent the vaginal orifice.
4. Brow presentation: Partially extended head most unfavourable presentation. Normal delivery is rarely possible if it does not change the attitude. The engaging diameter is mento vertical 13.5cm, Bitemporal 8.2cm and circumference is mento vertical 38cm.
Importance of the fetal skull to the midwife
1. It contains the delicate brain and about 95% of babies present by head.
2. Sound knowledge of fetal diameter and measurement cause least problems during labour and delivery through diagnosis of abnormalities presentation and position, also disproportion between the fetal head and the pelvis can be easily recognized.
3. Delivery can be conducted with minimal injuries to the mother and baby.
4. It is large in comparison with the fetal body and true pelvis; some adaptation has to be made between the head and the pelvis.
5. The head is the most difficult part to be delivered either it comes first or last.
The scalp
1. The scalp of the fetus consists of five layers.
2. The skin
3. A subcutaneous tissue: Contains blood vessels and hair follicles.
Is the part where caput succedaneum is formed.
4. A layer of Tendon – Galea
5. A loose layer of alveolar tissue. Limits movement of the 6. scalp over the skull.
7. The pericranium – is the periosteum of the cranial bones which covers the outer surface, and is adherent to their edge.
8. Cephalhaematoma is limited to the layer over the bones where it lays because it is attached to the edge of the bone.
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Internal Structure of the Fetal Skull
The skull contains delicate membranous structure which is liable to damage during delivery especially if subjected to abnormal molding.
Structures include:
i. Folds of Dura matter and
ii. Venous sinuses associated with them.
The membrane is in two layers, an outer periosteal layer which is adherent to the skull bones and the inner meningeal layer which covers the outer surface of the brain. The membrane does not only cover the brain but send fibrous partition to divide the brain into compartments.
1. The Falx Cerebri: It is a sickle-shaped fold of membrane which dip down between the two cerebral hemispheres. It runs beneath the frontal and sagittal sutures – (From root of the nose to the internal occipital protuberance).
2. Tentorium Cerebelli: This is a horizontal fold of dura matter situated at the posterior part of the cranial cavity. It lies at right
19:
20
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angle to the falx cerebri. It has a horse – shoe shape and forms a tent-like layer between the cerebrum and the cerebellum. It contains large blood vessels or sinus which drains blood from the brain on their way to become the jugular vein of the neck.
3. The superior Longitudinal(Sagittal) Sinus: it runs along the upper part of the falx corebri from front to the back (from root of the nose to the internal occipital protuberance).
4. Inferior Longitudinal (sagittal) Sinus: Runs along the lower part in the same direction.
5. The straight sinus: Is a continuation of the inferior sagittal sinus and drains blood from the great cerebral vain and the inferior sagittal sinus along the junction of falx and the tentorium. The point where it reaches the skull and receives blood from the superior sagittal sinus is known as the confluence of sinus.
6. The Great Cerebral vein of Galen: meet the inferior Sagittal Sinus at the inner end of the junction and where the falx joins the tentorium
7. Lateral Sinuses: These are two in number they pass from the onfluence of the sinuses along the outer edge of the tentorum cerebelli and carries blood to the internal jugular veins. During moulding the falx and the tentorium are stretched. The tentorium is most vulnerable to tear near its attachment to the falx – (Tentorial Tears), this leads to bleeding from the great cerebral vain giving rise to intracranial hemorrhage.
Moulding
This is the term applied to the change in shape of the fetal head which takes place as it passes through the birth canal. It is brought about by pressure between the fetal skull and the maternal pelvis. It results in compression of the movable bones and elongation of those which are not compressed. Moulding brings about a considerable reduction in the size of the presenting diameters while the diameter at right angle to them elongates. This is possible because of the sutures and fontanelles on the vault which allows slight degree of movement and the bones to override each other. In normal vertex presentation, the biperiatal diameter, sub occipito bregmatic reduce while the mentovertical lengthens. During moulding the anterior parietal bone override the posterior one, the frontal and occipital bones go under the parietal bones. The advantage of moulding is that it is a protective mechanism and prevents compression of the fetal brain, once it is not excessive, too rapid or unfavourable direction. The skull of a preterm baby may mould excessively while that of post mature does not mould which tend to make labour more difficult.
In certain types of moulding the internal structure maybe damage given rise to oedema or haemorrhage and congestion may give rise to mild
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cerebral irritation. This can lead to death or permanent brain damage.
These dangerous moulding includes:
1. Excessive moulding: In cases of prolonged labour, due to cephalo pelvic disproportion, prematurity.
2. Upward moulding: Occipito posterior position resulting in “face to Pubis” and after coming head of the breech.
3. Rapid moulding: Precipitate labour Rapid compression and decompression result in rupture of cerebral membranes.
SELF- ASSESSMENT EXERCISE
Which of the following statements is false? In each case, say why it is incorrect.
i. The iliac crest is an important landmark in measuring the progress of the fetus down the birth canal.
ii. The sutures in the fetal skull are strong hard joints that hold the skull bones rigidly in place.
iii. A newborn baby’s pulse can be seen beating in the anterior fontanel.
4.0 CONCLUSION
The skull bones encase and protect the brain, which is very delicate and subjected to pressure when the fetal head passes down the birth canal.
Correct presentation of the smallest diameter of the fetal skull to the largest diameter of the mother’s bony pelvis is essential if delivery is to proceed normally.
5.0 SUMMARY
The female reproductive system can be divided into two parts, the external genitalia known as the vulva which comprises of the vaginal, uterus, uterine tubes and the ovary. Each of these structures plays different roles but their focus is to bring about process of fertilization and delivery at the end of pregnancy. Menstruation is the discharge of blood from the uterus as a response to progesterone hormonal level in the blood stream. Every month the uterus is prepared ready to receive fertilized ovum. In the absence of pregnancy the corpus lueteum degenerates and menses occurs 14 days before the next one.
The male reproductive system is divided into 2 parts, the external and the internal. The external comprises the penis and scrotum. The internal structure lies within the body. The scrotum houses the testes while testes houses seminiferous tubules and gonads. Seminiferous cells contain the sperm cells in various stages of developments. The epididymis provides
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area for maturation of the sperm and acts as a reservoir for matured spermatozoa. Seminal fluids provide nutrition that aids motility and fertility ability of the sperm. Cowper’s glands secrete alkaline fluid which neutralizes acidic vaginal secretions. For effective performance of its function the testes has to be at lower temperature than that of the body.
The pelvis consists of four bones, two innominate bones, one sacrum and one coccyx, joined together by very strong fibrous band known as the ligament. The pelvis is divided into the false pelvis, which is of no significance to midwifery practice, and the true pelvis made up of important land marks. The most favourable type of pelvis for delivery is the gynaecoid. The pelvic floor is filled with muscles which hang down like a sling. It forms a good support for the pelvic and abdominal organs.
The fetal skull develops from membranes. At birth the bones are separated by membranous lines known as sutures. Where the sutures meet forms the fontanelles which are important landmarks in midwifery.
6.0 TUTOR-MARKED ASSIGNMENT
Working with your preceptors, examine the head of five new born in the nearest maternity center to you.
7.0 REFERENCES/FURTHER READING
Adele Pillitteri (2010) Maternal and Child Health Nursing: Care of the Child Bearing and Child Rearing Family. Lippincot Williams &
Wilkins, New York.
Fraser D.M. Cooper M.A. and Nolte A.G.W. (2006) Myles Textbook for Midwives African Edition.
Thresyamma C.P. (2002). A Guide to Midwifery Students. Jaypee Brothers Medical Publisher (P) Ltd. New Delhi.
Ojo O.A. and Briggs E.B. (2006) A Textbook for Midwives in the Tropics. 2nd ed. Jaypee Brothers Ltd. New Delhi.
DiDona N.A. and Marks M.G. (1996) Introductory Maternal Newborn Nursing Lippincott.
Ministry of Health. 2007. Malawi national reproductive health service delivery guidelines. Lilongwe, Malawi: Ministry of Health.
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Marieb, Elaine N. 2000. Essentials of human anatomy and physiology.
6th ed. San Francisco, CA: Benjamin/Cummings.
Tortora, Gerard J. and Sandra Reynolds Grabowski. 1993. Principles of anatomy and physiology. 7th ed. New York, NY: HarperCollins College.
World Health Organization/Department of Reproductive Health and Research (WHO/RHR) and Johns Hopkins Bloomberg School of Public Health/Center for Communications Programs (CCP), Knowledge for Health Project. Family Planning: A global handbook for providers (2008 update). Baltimore and Geneva:
CCP and WHO/RHR. (http://info.k4health.org/globalhandbook/ )
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