Obstetric Anatomy

1. Obstetric Anatomy Professor of Obstetrics & Gynecology Ain Shams Faculty of Medicine

2. The Fetal Skull Anatomy Diameters Molding Caput Succedaneum Cephalhematoma

3. The vault : From the orbital ridge to the nape of the neck (frontal, parietal, occipital bones). It is compressible. • The Face: Root of the nose to junction of head and neck.

5. Transverse Diameters of the Fetal Skull

6. 6

8. Fetal Skull Circumferences • The Suboccipito-Bregmatic X Bipareital (28 cm.) • These are the engaging diameters of well flexed vertex presentation. • Occipito-frontal X Biparietal (33 cm.) • These are the engaging diameters in deflexed vertex presentation ( OP position). • Mento-vertical X Biparietal (35.5 cm.) • This is the largest head circumference ( Brow presentation)

9. Engaging Diameters of Fetal Skull

10. Moulding… Reshaping of the fetal skull: Obliteration of the sutures. Overlapping of the bones of the vault: One parietal bone overlaps the other. Both overlap the occipital bone. It accounts for diminution of the biparietal diameter and suboccipitobregmatic diameters by 0.5-1 cm. 0r even more.

11. A: Well flexed Head • B: Partially Flexed Head • C: Deflexed Head • D: Face Presentation • E: Brow presentation

12. Superior long. Sinus Falx cerebri Inferior long sinus Vein of Galen Tentorium Cerebelli Overmoulding • Occurs in case of obstructed labor. • There is overstretch of the falx cerebri which tears from its attachment at the tentorium cerebelli. • Subsequently there is injury of the vein of Galen with ICH.

13. The Scalp Tissues • There are Five layers of scalp tissue • Skin: The outer covering containing hair. • Subcutaneous tissue • Muscle Layer: containing the tendon of Galae. • Connective tissue: a loose layer. • Periosteum: covers the skull bones and attached at the suture line

14. Diffuse scalp edema resulting from venous congestion due to prolonged pressure on the fetal head by the pelvic bones. It is soft and boggy to touch It usually disappears Localized caput…? It is usually few mm. Thick but may be large and lead to misinterpretation of the station of the head. The presence of caput may have medico-legal implication: The baby was living Labor was difficult D.D…Cephalhematoma Caput Succedaneum

15. Cephalhematoma • This swelling is due to bleeding between the skull bone and periosteum. • Bleeding occurs due to friction between the overriding bones and periosteum during molding. • It is just as likely to occur during a normal delivery as during more difficult labor. • A low prothrombin level is probably a contributory cause

16. Caput Succedaneum Cephalhematoma • Cephalhematoma is not present at birth but appears 2-3 days. • The swelling is limited by the periosteum. It therefore can NOT lie over a suture. • The head is more red ad bruised in appearance than in caput succedaneum. • The swelling may increase and it takes 6 weeks at least to disappear.

17. The Female Pelvis Anatomy Pelvic Diameters Pelvic Types

18. The Female Pelvis • Four Bones articulated at Four Joints. • False pelvis: above the pelvic brim and has no obstetric importance. • True pelvis: below the pelvic brim. It is the bone defined tunnel that the infant must traverse at birth.

20. Ilio-pectineal line Ischial spine SP Ischial tuberosity

21. SP Ischial Spine Ischial Tuberosity

22. The Planes of the pelvis • Plane of the pelvic inlet. • Plane of the cavity: Plane of greatest Pelvic Dimensions • Plane of the mid pelvis (plane of obstetric outlet) • Plane of the Anatomical outlet

23. Plane Of The Pelvic Inlet • passing with the boundaries of pelvic brim and making an angle of 55o with the horizon (angle of pelvic inclination).

24. Plane of the Pelvic Cavity • It is the plane of greatest pelvic dimensions. • It passes between the middle of the posterior surface of the symphysis pubis and the junction between 2nd and 3rd sacral vertebrae. Laterally, it passes to the centre of the acetabulum and the upper part of the greater sciatic notch. • It is a round plane with diameter of 12.5 cm. • Internal rotation of the head occurs when the biparietal diameter occupies this wide pelvic plane while the occiput is on the pelvic floor i.e. at the plane of the least pelvic dimensions.

25. Plane Of Obstetric Outlet • It is the plane of least pelvic dimensions. • It passes from the lower border of the symphysis pubis anteriorly, to the ischial spines laterally, to the tip of the sacrum posteriorly. • It is the plane of the pelvic floor. • The head is considered engaged if the vault reaches it. • This is the plane where the pelvic axis turns forwards.

26. Plane Of Anatomical Outlet • It passes with the boundaries of anatomical outlet and consists of 2 triangular planes with one base which is the bituberous diameter. • Anterior sagittal plane: its apex at the lower border of the symphysis pubis. • Anterior sagittal diameter from the lower border of the symphsis pubis to the centre of the bituberous diameter: 6-7 cm • Posterior sagittal plane: its apex at the tip of the coccyx. • Posterior sagittal diameter from the tip of the sacrum to the centre of the bituberous diameter: 7.5-10 cm

27. The consequences of walking upright… • When a women stands erect: • The pelvic inlet makes an angle of about 55° with the horizon. • The pelvic outlet makes an angle of 15° with the horizon • If the angle made by the inlet is greater than 55° this may make the descent of the fetal head in the pelvis difficult.

28. The Obstetric Pelvic Axis • This represents the path that the presenting part must follow for delivery to occur: • The upper part moves downward approximately in a straight line till the level of the ischial spine. • The trajectory then changes to become a curvilinear path directed forward and downward

29. At the level of the Ischial Spine • The plane of obstetric outlet (plane of the least pelvic dimensions). • The levator ani muscles. • The obstetric axis of the pelvis changes its direction. • The head is considered engaged when the vault is felt vaginally at or below this level. • Internal rotation of the head occurs when the occiput is at this level. • Forceps is applied only when the head at this level (mid forceps) or below it ( low and outlet forceps). • Pudendal nerve block is carried out at this level. • Normal level of the external os of the cervix.

30. The truth is that the majority of the pelves are a mixture of all the 4 types. Four types of Female PelvisThe Caldwell-Moloy’s classification • They differ in: • Shape of the pelvic inlet • Shape of the side-walls • Character of the subpubic arch • Four types do exist: • Gynecoid: 50%. • Android: 20%. • Anthropoid: 25%. • Platypelloid: 5%.

31. Android Gynecoid • Rounded • Trans. Diameter Slightly behind the centre • Heart shaped • Trans. Diameter Near the sacrum Platypelloid Anthropoid • Wide Trans. diameter • AP diameter>Trans.

32. Types of female Pelvis

34. The True Conjugate = 11 cm The Obstet. Conjugate = 10.5cm The Diagonal Conjugate = 12 cm

35. Diameters of the Inlet

38. Interspinous diam. = 10.5 cm. Anato. Ant. Post diam= 11 cm. Obstet. Ant. Post diam= 13 cm.

39. Diameters of the Outlet

40. Tom’s Dictum: If the sum of the Bituberous diameter and Post. Sagittal diameter is less than 15, the pelvic outlet is contracted . This is an indication of performing a Cesarean section.

41. Anterior Sagittal Plane Posterior Sagittal Plane The Plane of the Outlet

42. Pelvic Soft Tissues The Formation Of The Lower Uterine Segment The Levatores Ani The Perineal Muscles Formation of the birth canal during labor The Episiotomy

43. The formation of the lower uterine segment • It is the part between the vesico-uterine fold of peritoneum superiorly and the cervix inferiorly. • It develops as early as the 16th week by incorporating the upper part of the cervix in the lower part of the uterus to accommodate for the presenting part of the fetus.

44. Differentiation of the Uterine Segments • The passive lower segment is derived from the isthmus. • The physiologic retraction ring develops at the junction of upper and lower uterine segments. • The Pathologic retraction ring develops from the physiologic ring in case of obstructed labor

46. Formation of the Birth Canal During Labor • The lower uterine segment, cervix and vagina become a single canal that allow for the passage of the baby to the outside. • Hypertrophy of the vaginal muscle layer and unfolding of the rugae allow for the accommodation of the fetus without damage.

47. Level of Internal os Formation of the Birth Canal During Labor • The cervix is obliterated, taken-up or effaced: It is reduced from a length of 2-2.5 cm to a mere paper thin circular orifice. • The lower uterine segment, cervix and vagina become a single canal that allow for the passage of the baby to the outside. • Hypertrophy of the vaginal muscle layer and unfolding of the rugae allow for the accommodation of the fetus without damage.

48. The Levatores Ani • A hammock of muscle sweeping down from the pelvic brim and investing the urethra, vagina and rectum. • Two gaps: • An anterior gap bridged by the urogenital diaphragm transmitting the urethra and vagina. • A posterior gap transmits the rectum and anal canal.

49. The resistance and shape of the pelvic floor play an important role in facilitating rotation and flexion of the presenting part. • As the presenting part descends: • The anterior portion of the pelvic floor is pressed outwards against the SP. • The posterior part becomes stretched into a thin-walled tube. • The perineal body stretches and thins from 5 cm. To 0.05 cm. and is displaced downward.