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1. DBU Asrat woldeyes health science campus Department of midwifery Fetal skull and Fetal Circulation By: Assalif B. ( MSc; Assistant professor in clinical midwifery) 4/20/2024 1

2. Fetal skull anatomy and fetal circulation Learning objective At the end of this session the students will able to: Discuss the anatomy of fetal skull Differentiate fetal skull landmarks Discuss the physiology of fetal circulation 4/20/2024 2

3. The fetal skull 3 4/20/2024 3

4. The fetal skull Is a bony box like cavity which contains and protects the delicate brain. It is the most important part of the fetus because; It contain the delicate brain It is the least compressible part of the fetus. It is the most difficult part to deliver whether it comes first or last. It is the largest part of fetus . 4/20/2024 4

5. The fetal skull… Division The fetal skull is divided into three parts: The vault – is the large dome shaped part above the imaginary line drown from below the occipital protuberance to the orbital ridges. The face - area extending from the orbital ridges to the junction of the chin and neck. The base - is composed of bones which are firmly united to protect the vital centers in the medulla. 4/20/2024 5

6. The fetal skull… Bones of the vault There are five main bones in the vault of the fetal skull. One occipital bones – lies at the back of the head and forms the region of the occiput . Its ossification center is known as occipital protuberance. It is roughly triangular in shape. In its lower part it forms the margins of the foramen magnum. 4/20/2024 6

7. The fetal skull… Two parietal bones – lie on either side of the skull. The ossification center of each bone is called partial eminence. They are the largest of the cranial bones. Roughly square in shape and curves as they lie over the parietal lobes of the brain. Two frontal bones – form the forehead or sinciput . Their ossification centers are named frontal eminence or frontal bones. Fuse in to a single bone by 8 years. 4/20/2024 7

8. The fetal skull… Sutures Is an area of membrane between the skull bones where ossification has not been completed. Overlap during the process of moulding at the time of birth. Types of sutures Lambdoidal suture – separate the occipital bone from the two parietal bones. It is shaped like the Greek letter Lambda . Sagital suture- runs between the two parietal bones and runs from the anterior fontanel in front to the posterior fontanel behind. Frontal sutures- runs between the frontal bones, extending from the root of nose below, to the anterior fontanel above. Coronal suture- separate frontal bones to parietal bones, passing from one temporal bones to the other. 4/20/2024 8

9. Fontanels Are areas where two or more suture meet. There are 6 fontanels, but only two are of great obstetrical importance. The anterior fontanel or bregma :-is formed where the sagital , coronal and frontal sutures meet. It is diamond in shape. It is much longer than posterior fontanel. Pulsation of cerebral vessels can be felt through it. Normally closes at 18 months of age 9 4/20/2024 9

10. Con’t … Posterior fontanel occurs at the junction of the lambdoidal and sagittal sutures. It is very small and triangular in shape. It is normally closes by 6 weeks of age. 4/20/2024 10

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12. Con’t .… The Regions of the skull Vertex –is bounded by the anterior and posterior fontanels and parietal eminences. Occiput – lies between the foramen magnum and posterior fontanel. Sinciput (brow) – extends from the anterior fontanel and coronal suture to the orbital ridge. Face – extends from the orbital ridges and the root of the nose to the junctions of the chin and neck. The point between the eye brow is known as the glabella . 4/20/2024 12

13. The fetal skull … Land marks of the fetal skull Occiput Vertex Sinciput Posterior fontanel (Lambda) Glabella Mentum (chin) Anterior fontanel ( Bregma ) Occipital protuberance 4/20/2024 13

14. Con’t … Diameters of the fetal skull Transverse Diameters Biparietal diameter- between the parietal eminences and measures 9.5cm Engagement occur as this diameter pass through the plane of the brim. Bi- temporal diameter – runs between the two extremities of the coronal sutures and is 8.2cm in length. Super- subparietal - : It extends from a point placed below one parietal eminence to a point placed above the other parietal eminence of the opposite side and measure 8.5 cm Bimastoid diameter : It is the distance between the tips of the mastoid processes and measure 7.5 cm . 4/20/2024 14

15. Transverse Diameters of fetal skull 4/20/2024 15

16. The fetal skull… Anteroposterior or longitudinal diameters Subocipitobregmatic - measured from below the occiput to the bregma . It measures 9.5cm. Suboccipito frontal – measured from below occipital protuberance to the center of the frontal sutures, and measures 10cm. Occipito frontal – measured between the occiput and the glabella . It is 11.5 cm in length Mento -vertical –extends from the midpoint of the chin to the highest point on the sagittal suture and it measures 13.5cm. 4/20/2024 16

17. The fetal skull… Submento vertical – measured from the point where the chin joins the neck to the highest point on the vertex. It is 11.5 cm in length. Submentobregmatic - measure from the point where the chin joins the neck to the center of the bregma and measures 9.5 cm. 4/20/2024 17

18. Antero-posterior or longitudinal diameters fetal skull 4/20/2024 18

19. Con’t … The scalp tissue There are five layers of scalp tissue : Skin containing hairs, (outer covering) Subcutaneous tissue. Muscle layer – containing the tendon of Galea . Connective tissue – a loose layer. Periosteum – which covers the skull bones. 4/20/2024 19

20. Con’t … Two conditions involving these tissue can arise during labor and both cause a swelling on the infant’s head. 1.Caput succedaneum – is an edematous swelling of the sub-cutaneous tissues of the fetal skull. It occurs in early rupture of membranes in the 1 st stage of labor, because there is no bag of fore waters to take the pressure of dilating cervix of the fetal head. 4/20/2024 20

21. The fetal skull… Characteristics It is present at birth. Occurs on the part of the head. It may lie over a suture line. It pits on pressure. It disappears with in 24 - 48hrs. No treatment required unless it is excessive. 4/20/2024 21

22. The fetal skull… 2.Cephalo hematoma – this swelling is due to bleeding between the skull bone and periosteum which covers it. The bleeding occurs because of friction between the skull bones and the periosteum . Characteristics It is not present at birth, but appears 2-3 days after wards. The swellings is limited by the periosteum and can there fore only occur over the bone, although it may be bilateral. It can not lie over a suture. 4/20/2024 22

23. Con’t… The head is usually red- and bruised in appearance. It takes 6 weeks to disappear completely . Treatment is only required if the hematoma increase in size over a number of days. RX- vit . K, injection to raise the prothrombin level and assist clotting . 4/20/2024 23

24. Con’t … Moulding :- Gradual overlapping of the vault bone as the skull is compressed during its passage in the birth canal It is an important indication on how adequately the pelvis can accommodate the fetal head Degree of molding - The cranial bones are separate along the suture lines + - Fetal cranial bones are touching each other along the suture lines ++ - Fetal cranial bones are overlapping but can be separated +++ -Fetal cranial bones are overlapping & are not separable 4/20/2024 24

25. Fetal Circulation In the fetal circulation, the right and left ventricles exist in a parallel circuit, as opposed to the series circuit of a newborn or adult. In the fetus, the placenta provides for gas and metabolite exchange. The lungs do not provide gas exchange, and vessels in the pulmonary circulation are vasoconstricted . Three cardiovascular structures unique to the fetus are important for maintaining this parallel circulation: ductus venosus , foramen ovale , and ductus arteriosus. 4/20/2024 25

26. Fetal Circulation cont… The umbilical vein transports blood rich in oxygen and nutrients from the placenta to the fetal body. This vein travels along the anterior abdominal wall of the fetus to the liver and at the porta hepatis , the umbilical vein divides in to two branches. Some of the blood passes in to the liver and the rest enters a shunting vessel called the ductus venosus that by passes the liver. The ducts venosus travels a short distance and joins the inferior vena cava. 4/20/2024 26

27. Fetal Circulation cont… H ere , the oxygenated blood from the placenta is mixed with deoxygenated blood from the lower parts of the fetal body. This blood continues through the vena cava to the right atrium. As the blood relatively high in oxygen enters the right atrium of the fetal heart, a large proportion of it is shunted directly in to the left atrium through an opening in the artial septum called the foramen ovale . The more highly oxygenated blood that enters the left atrium through the foramen ovale is mixed with a small amount of deoxygenated blood returning from the pulmonary veins. This mixture moves in to the left ventricle and is pumped in to the aorta. 4/20/2024 27

28. Fetal Circulation cont… Some of this blood reaches the myocardium by means of the coronary arteries and some reaches the tissues of the brain through the carotid arteries. The rest of the blood entering the right atrium as well as the large proportion of the deoxygenated blood entering from the superior vena cava, passes in to the right ventricle and out through the pulmonary artery. 4/20/2024 28

29. Fetal Circulation cont… Enough blood reaches the lung tissues to sustain them. Most of the blood in the pulmonary artery bypasses the lungs by entering the ductus arterious which connects the pulmonary artery to the descending portion of the aortic arch. Some of the blood carried by the descending aorta leads to the various parts in the lower regions of the body. The rest of the blood passes in to the umbilical arteries which branch from the internal iliac arteries and lead to the placenta. 4/20/2024 29

30. Fetal Circulation cont… CIRCULATION CHANGES AFTER BIRTH The umbilical vein is obliterated and become the round ligament of the liver. The umbilical arteries are obliterated and ultimately become ligaments. The ductus venosus is obliterated and become a ligament. Anatomic closure is completed at the end of 2 months. 4/20/2024 30

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32. Fetal Circulation cont… Conversion of Fetal to Infant Circulation At birth Clamping the cord shuts down low-pressure system. Increased atmospheric pressure (increased systemic vascular resistance) causes lungs to inflate with oxygen. Lungs now become a low-pressure system. Pressure from increased blood flow. 4/20/2024 32

33. Fetal Circulation cont… In the left side of the heart causes the foramen ovale to close. More heavily oxygenated blood passing by the ductus arteriosus causes it to constrict. Functional closure of the foramen ovale and ductus arteriosus occurs soon after birth. Overall anatomic changes are not complete for weeks. 4/20/2024 33

34. Adult remnants of fetal circulation Adult Fetus Fossa ovale Foramen ovale Ligamentum arteriosum Ductus arteriosus Medial umbilical ligaments Umbilical aa.(within fetus) Round ligament (ligamentum teres) of liver Umbilical v.(within fetus) Ligamentum venosum Ductus venosus Medial umbilical ligament Umbilical cord (leaving fetus) 4/20/2024 34

35. Blood Flow Before Delivery Blood vessels are constricted Blood flow in the lungs is decreased Blood flow is diverted across the ductus arteriosus Fluid in air sacs Right atrium Right ventricle Left ventricle 4/20/2024 35

36. Blood Flow Changes at Birth Lungs expand with air Fetal lung fluid leaves air sacs Fluid replaced by air in air sacs 4/20/2024 36

37. Blood Flow Changes at Birth Umbilical cord clamped Blood flow in the lungs increases Blood vessels in the lung tissue relax Fluid in air sacs Oxygen in air sacs 4/20/2024 37

38. Normal Transition No meconium Breathing/crying Good muscle tone Term 4/20/2024 38

39. Premature Infants at Higher Risk Immature lungs – increased respiratory distress Increased heat loss and poor temperature control Possible infection Prone to bleeding in the brain Feeding problems 4/20/2024 39

40. References DC Dutta’sTextbook of OBSTETRICS 8 th edition Williams obstetrics 26 th edition 4/20/2024 40

41. THANK YOU!!! 4/20/2024 41