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Fetal head, maternal pelvis & pelvimetry

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Fetal head & maternal bony pelvis diameters. …

Fetal head & maternal bony pelvis diameters.
Clinical pelvimetry.


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  • sacral promontory (anterior and upper margin of the first sacral vertebra)the iliopectineal lines (a line that runs downward and forward around the inner surface of the ileum)
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    • 1. Prepared by: Amaal Atta El-Seqali Rasha Khamis El-Dabbagh
    • 2. P’S IN LABOR & DELIVERY 1.Passenger= The fetus 2. Passageway= The birth canal 3. Power of labor= Force of uterine contractions 4. Placenta 5. Psyche
    • 3. Anatomic characteristic of the fetal head & maternal pelvis
    • 4. Objectes • Fetal head • Pelvic anatomy • Pelvic shapes • Pelvimetry • Cephalopelvic disproportion
    • 5. Fetal head • Sutures • Fontanelles • Landmarks • Diameters
    • 6. Fetal head From an obstetrical point of view it’s the most important part: • largest • least compressible part of the fetus. • most frequent presenting part
    • 7. consists of: 1-Base: large, ossified, firmly united, and noncompressible 2-vault (cranium) consists of: -occipital bone posteriorly - 2 parietal bones bilaterally -2 frontal and temporal bones anteriorly
    • 8. Cranial bones at birth: • Thin • weakly ossified • easily compressible • interconnected only by membranes >>> allow them to overlap under pressure & to change shape to conform to the maternal pelvis, a process known as (molding).
    • 9. Sutures • Membrane-occupied spaces between the cranial bones 1-Sagittal suture: - lies btw the parietal bones -extends in an AP direction btw the fontanelles -divides the head into right and left sides
    • 10. 2-lambdoid suture: • extends from the posterior fontanelle laterally • separate the occipital from the parietal bones.
    • 11. 3-coronal suture: • extends from the anterior fontanelle laterally • separate the parietal and frontal bones.
    • 12. 4- frontal suture: • lies between the frontal bones • extends from the anterior fontanelle to the glabella (the prominence between the eyebrows).
    • 13. Clinical importance of sutures • molding of the head in the vertex presentation • Position of fontanelle & sagittal suture can identify attitude and position of vertex. • By plapating the sagittal suture during labour, degree of internal rotation & molding of the head can be noticed. • In deep transverse arrest, this sagittal suture lies transversely at the level of the ischial spines.
    • 14. Fontanelles • membrane-filled spaces located at the point where the sutures intersect • more useful in diagnosing the fetal head position than the sutures.
    • 15. The anterior fontanelle (bregma) :  diamond shaped area(2 × 3 cm) of unossified membrane formed by the junction of 4 suture. The suture are:- Anteriorly: frontal suture Posteriorly: sagittal suture Laterally: on both side:-coronal suture.  It is felt on fetal head surface as a soft shallow depression.  It ossifies by 18 months after birth.>>>allows the skull to accommodate the tremendous growth of the infant's brain after birth
    • 16. Clinical importance: 1. Degree of flexion can be assessed from its position. If on vaginal examination it is felt easily, it indicates the head is not well flexed. 2. Helps in the molding of head. 3. Internal rotation of the head can be assessed from it’s position. 4. ICP can be roughly assessed from its condition after birth. Depression in dehydration and bulging in raised ICP. 5. CSF can be collected from its lateral angles from the lateral ventricles.
    • 17. The posterior fontanelle:  It is the triangular depressed area at the junction of 3 suture: Anteriorly: sagittal suture Posteriorly: 2 lambdoid sutures at both side. • closes at 6 to 8 weeks of life • Y- or T-shaped
    • 18. Clinical importance: 1. From its relation of the maternal pelvis, position of vertex is determined. 2. Internal rotation can be assessed from its location. 3. Degree of flexion can be assessed from its position. On vaginal examination if it is felt easily and anterior fontanelle is not felt, this indicates good flexion of the fetal head.
    • 19. landmarks front to back 1. Nasion (the root of the nose) 2. Glabella (the elevated area btw the orbital ridges) 3. Sinciput (brow) (the area btw AF & glabella)
    • 20. 4-Anterior fontanelle (bregma) 5-Vertex (the area btw the fontanelles & bounded laterally by the parietal eminences) 6-Posterior fontanelle (lambda) 7-Occiput (the area behind & inferior to PF & lambdoid sutures)
    • 21. Diameters 6 • Anteroposterior diameters (4): presenting to the maternal pelvis depends on the degree of flexion or extension of the head • Transverse diameters (2)
    • 22. Anteroposterior diameters 1- Suboccipitobregmatic (9.5 cm): Extends from the undersurface of the occipital bone at the junction with the neck to the center of the AF.
    • 23. • Present AP diameter when the head is well flexed >>>> OT or OA position LOAROT
    • 24. ROT LOT
    • 25. LOAROA
    • 26. 2. Occipitofrontal (11 cm): • extends from the external occipital protuberance to the glabella.
    • 27. • presenting AP diameter when the head is deflexed >>> OP
    • 28. LOP ROP LOP
    • 29. 3. Supraoccipitomental (13.5 cm): • extends from the vertex to the chin
    • 30. -presenting AP diameter in a brow presentation -longest AP diameter of the head
    • 31. 4. Submentobregmatic (9.5 cm): • extends from the junction of the neck and lower jaw to the center of the anterior fontanelle.
    • 32. -presenting AP diameter in face presentations
    • 33. Transverse diameters 1-Biparietal (9.5 cm): • the largest transverse diameter • extends btw the parietal bones. 2-Bitemporal (8 cm): • the shortest transverse diameter • extends btw the temporal bones.
    • 34. Pelvic anatomy • Bony pelvis • Pelvic planes • Pelvic diameters
    • 35. The bony pelvis four bones : • two hip bones(ileum, ischium & pubis) laterally & anteriorly • sacrum & coccyx posteriorly ‘3 joints’ • symphysis pubis anteriorly • sacroiliac joints posteriorly
    • 36. Sacrum • consists of 5 rudimentary vertebrae fused together to form a single wedge-shaped bone with a forward concavity • The upper border ( base) articulates with the L5 • The narrow inferior border articulates with the coccyx. • Laterally, the sacrum articulates with the two iliac bones • The anterior and upper margins of the first sacral vertebra bulge forward sacral promontory
    • 37. Coccyx • consists of 4 vertebrae fused together to form a small triangular bone • articulates at its base with the lower end of the sacrum • It’s vertebrae consist of bodies only, but the first vertebra possesses a rudimentary transverse process and cornua. The cornua are the remains of the pedicles and superior articular processes and project upward to articulate with the sacral cornua
    • 38. Hip Bone In children: each hip bone consists of : • the ilium, which lies superiorly • the ischium, which lies posteriorly and inferiorly • the pubis, which lies anteriorly and inferiorly  joined by cartilage at the acetabulum  At puberty, >>> fuse together to form one large, irregular bone.  articulate with the sacrum at the sacroiliac joints >>>>form the anterolateral wall of the pelvis  articulate with one another anteriorly at the symphysis pubis.
    • 39. The ilium,  the upper flattened part of the hip bone • iliac crest runs between the anterior and posterior superior iliac spines • Below these spines are the corresponding anterior and posterior inferior iliac spines • The iliopectineal line runs downward and forward around the inner surface of the ilium and serves to divide the false from the true pelvis.
    • 40. The ischium  the inferior and posterior part of the hip bone • ischial spine • ischial tuberosity
    • 41. 3-The pubis  the anterior part of the hip bone • Body bears pubic crest & pubic tubercle and articulates with the pubic bone of the opposite side at the symphysis pubis • superior and inferior pubic rami
    • 42. Pelvic brim is formed by: • the sacral promontory behind, • iliopectineal lines laterally, • symphysis pubis anteriorly. • Above the brim >>> false pelvis, which forms part of the abdominal cavity. • Below the brim >>> true pelvis.
    • 43. False Pelvis bordered by: • lumbar vertebrae posteriorly • iliac fossa bilaterally • abdominal wall anteriorly. supports the abdominal contents after 1st trimester helps support the gravid uterus.
    • 44. True Pelvis bony canal and is formed by: • the sacrum and coccyx posteriorly • the ischium and pubis laterally and anteriorly  It’s internal borders are solid and relatively immobile.  The posterior wall is twice the length of the anterior wall.  The area of concern to the obstetrician because its dimensions are sometimes not adequate to permit passage of the fetus.
    • 45. Pelvic Planes • imaginary, flat surfaces that extend across the pelvis at different levels. four planes : 1. The pelvic inlet 2. The plane of greatest diameter 3. The plane of least diameter 4. The pelvic outlet
    • 46. 1-The plane of the inlet: bordered by: • pubic crest anteriorly • iliopectineal line of the innominate bones laterally • promontory of the sacrum posteriorly. fetal head enters the pelvis through this plane in the transverse position.
    • 47. 2-The plane of greatest diameter: • largest part of the pelvic cavity bordered by: • the posterior midpoint of the pubis anteriorly • the upper part of the obturator foramina laterally • the junction of the 2nd and 3rd sacral vertebrae posteriorly. The fetal head rotates to the anterior position in this plane
    • 48. 3-The plane of least diameter: the most important from a clinical standpoint, because most instances of arrest of descent occur at this level. bordered by: • the lower edge of the pubis anteriorly • the ischial spines and sacrospinous ligaments laterally • the lower sacrum posteriorly. Low transverse arrests generally occur in this plane.
    • 49. 4-The plane of the pelvic outlet : is formed by 2 triangular planes with a common base at the level of the ischial tuberosities. The anterior triangle is bordered by: • the subpubic angle at the apex, • the pubic rami on the sides, • the bituberous diameter at the base. The posterior triangle is bordered by: • the sacrococcygeal joint at its apex, • the sacrotuberous ligaments on the sides, • and the bituberous diameter at the base. This plane is the site of a low pelvic arrest.
    • 50.  represent the amount of space available at each level.  The key measurements for assessing the capacity of the maternal pelvis include the following: 1. The obstetric conjugate of the inlet 2. The bispinous diameter 3. The bituberous diameter 4. The posterior sagittal diameter at all levels 5. The curve and length of the sacrum 6. The subpubic angle Pelvic Diameters
    • 51. pelvic inlet 5 important diameters: 1-The true conjugate (anatomic conjugate) the anatomic diameter and extends from the middle of the sacral promontory to the superior surface of the pubic symphysis. 2-The obstetric conjugate the actual space available to the fetus and extends from the middle of the sacral promontory to the closest point on the convex post. surface of the symphysis pubis.
    • 52. 3-The transverse diameter : the widest distance between the iliopectineal lines. 4-Each oblique diameter: extends from the sacroiliac joint to the opposite iliopectineal eminence. 5-The posterior sagittal diameter: extends from the AP and transverse intersection to the middle of the sacral promontory
    • 53. Greatest Diameter 2 diameters: 1- The AP diameter: extends from the midpoint of the posterior surface of the pubis to the junction of the 2nd and 3rd sacral vertebrae 2-The transverse diameter: The widest distance btw the lateral borders of the plane
    • 54. Least Diameter (Midplane) • 3 important diameters: 1-The AP diameter: extends from the lower border of the pubis to the junction of the 4th & 5th sacral vertebrae 2-The transverse (bispinous) diameter: extends btw the ischial spines 3- The posterior sagittal diameter: extends from the midpoint of the bispinous diameter to the junction of the 4th & 5th sacral vertebrae.
    • 55. Pelvic Outlet • 4 important diameters: 1-The anatomic AP diameter: extends from the inferior margin of the pubis to the tip of the coccyx 2-obstetric AP diameter: extends from the inferior margin of the pubis to the sacrococcygeal joint. 3-The transverse (bituberous) diameter: extends btw the inner surfaces of the ischial tuberosities, 4-Post. sagittal diameter: extends from the middle of the transverse diameter to the sacrococcygeal joint.
    • 56. Pelvic Shapes & Pelvimetry By: Rasha Khamis Al-Dabbagh Amaal Atta El-Seqali
    • 57. Pelvic Shapes
    • 58. Gynecoid Pelvis • The classic female type. • Found in approximately 50% of women. • Characteristics: 1. Round inlet, with the widest transverse diameter only slightly greater than the AP diameter 2. Side walls straight 3. Ischial spines of average prominence . 4. Well-rounded sacrosciatic notch 5. Well-curved sacrum 6. Spacious subpubic arch, with an angle of approximately 90 degrees
    • 59. • These features create a cylindrical shape that is spacious throughout. • The fetal head generally rotates into the occipitoanterior position in this type of pelvis.
    • 60. Android Pelvis • The typical male type • Found in less than 30% of women • Characteristics: 1. Triangular inlet with a flat posterior segment & the widest transverse diameter closer to the sacrum than in the gynecoid type . 2. Convergent side walls with prominent spines 3. Shallow sacral curve 4. Long and narrow sacrosciatic notch 5. Narrow subpubic arch
    • 61. • Limited space at the inlet & progressively lessens down the pelvis, owing to the funneling effect of the side walls, sacrum, and pubic rami. • Restricted space at all levels. • The fetal head is forced to be in the occipitoposterior position to conform to the narrow anterior pelvis. • Arrest of descent is common at the midpelvis.
    • 62. Anthropoid Pelvis • Resembles anthropoid ape pelvis. • Found in approximately 20% of women • Characteristics: 1. A much larger AP than transverse diameter, creating a long narrow oval at the inlet 2. Side walls that do not converge 3. Ischial spines that are not prominent but are close, owing to the overall shape 4. Variable, but usually posterior, inclination of the sacrum 5. Large sacrosciatic notch 6. Narrow, outwardly shaped subpubic arch
    • 63. • The fetal head can engage only in the AP diameter and usually does so in the occipitoposterior position, because there is more space in the posterior pelvis.
    • 64. Platypelloid Pelvis • Flattened gynecoid pelvis. • Found in only 3% of women • Characteristics: 1. A short AP & wide transverse diameter creating an oval- shaped inlet 2. Straight or divergent side walls 3. Posterior inclination of a flat sacrum 4. A wide bispinous diameter 5. A wide subpubic arch • The fetal head has to engage in the transverse diameter.
    • 65. PELVIMETRY • Pelvimetry is the assessment of the dimensions & capacity of adult female pelvis in relation to the birth of a baby. • Pelvimetry was heavily used in leading the decision of natural, operative vaginal delivery or CS.
    • 66. Types of Pelvimetry External/indirect pelvimetry – Measures diameters of false pelvis – Little value, unreliable, no longer used Internal/ direct pelvimetry Radiographic pelvimetry
    • 67. Internal Pelvimetry • Through vaginal examination • At first prenatal visit screen for obvious contractions. • In late pregnancy (preferred) – After 37 weeks GA or at the onset of labour – the soft tissues are more distensible – more accurate – less uncomfortable
    • 68. Pelvic Inlet 1. Palpation of pelvic brim: • The index & middle fingers are moved along the pelvic brim. • Note whether round or angulated, causing the fingers to dip into a V-shaped depression behind the symphysis.
    • 69. 2) Diagonal conjugate: • Measured from the lower border of the pubis to the sacral promontory using the tip of the second finger and the point where the index finger of the other hand meets the pubis • Normally 12.5 cm & cannot be reached. • If it is felt the pelvis is contracted • True conjugate = diagonal conjugate – 1.5 • Not done if the head is engaged.
    • 70. The Midpelvis 1) Symphysis: – Height, thickness & curvature 2) Sacrum: – Shape & curvature – Concave usually. – Flat or convex shape may indicate AP constriction throughout the pelvis. 3) Side walls: – Straight, convergent or divergent starting from the pelvic brim down to the base of ischial spines. – Normally almost parallel or divergent
    • 71. 4) Ischial spines prominence: – The ischial spines can be located by following the sacrospinous ligament to its lateral end. – Blunt (difficult to identify at all), – Prominent (easily felt but not large) or – Very prominent (large and encroaching on the mid-plane). 5) Interspinous diameter: – If both spines can be touched simultaneously, the interspinous diameter is 9.5 cm i.e. inadequate for an average- sized baby.
    • 72. 6) Sacrospinous ligament: – Its length is assessed by placing one finger on the ischial spine & one finger on the sacrum in the midline. – The average length is 3 fingerbreadths. 7) Sacrosciatic notch: – If the sacrospinous ligament is 2.5 fingers, the sacrosciatic notch is considered adequate. – Short ligament suggests forward curvature of the sacrum & narrowed sacrosciatic notch.
    • 73. Pelvic Outlet 1) Subpubic angle: –Assessed by placing a thumb next to each inferior pubic ramus and then estimating the angle at which they meet. –Normally, it admits 2 fingers. (90o) –Angle ≤ 90 degrees suggests contracted transverse diameter in the midplane and outlet.
    • 74. 2) Mobility of the coccyx. – by pressing firmly on it while an external hand on it can determine its mobility. 3) Anteroposterior diameter of the outlet: – From the tip of the sacrum to the inferior edge of the symphysis. (>11cm)
    • 75. 4) Bituberous diameter: –Done by first placing a fist between the ischial tuberosities. –An 8.5 cm distance (4 knuckles) is considered to indicate an adequate transverse diameter.
    • 76. Adequate Pelvis Data Finding Forepelvis (pelvic brim) Round. Diagonal conjugate ≥ 11.5 cm. Symphysis Average thickness, parallel to sacrum. Sacrum Hollow, average inclination. Side walls Straight. Ischial spines Blunt. Interspinous diameter ≥ 10.0 cm. Sacrosciatic notch 2.5 -3 finger - breadths. Subpubic angle 2fingerbreadths (90o). Bituberous diameter 4 knuckles (> 8.0 cm). Coccyx Mobile. Anterposterior diameter of outlet ≥ 11.0 cm.
    • 77. Radiological Pelvimetry • X-ray: – Limited value. No role in guiding management. • CT: – Ease of performance, interpretation, & 10% less radiation exposure to the fetus . – Can evaluate fetal lie & position. • MRI (method of choice): – Lack of ionizing radiation, higher resolution & contrast but also higher cost.
    • 78. • Indications : 1. Clinical evidence or obstetric history suggestive of pelvic abnormalities. 2. A history of pelvic trauma.
    • 79. • CT pelvimetry. Breech presentation. A. Anteroposterior view is used to measure the transverse diameter of the pelvic inlet (≥ 11.5 cm). B. Lateral view is used to measure the anteroposterior diameter of the inlet (≥10 cm) & midpelvis. C. Axial view at the level of the fovea of the femoral heads is used to measure the bi-ischial diameter (≥ 9.5 cm)
    • 80. MRl pelvimetry with AP inlet and outlet measurements.
    • 81. Cephalometry • Ultrasonography: is the safe, accurate and easy method and can detect: – The biparietal diameter (BPD). – The occipito-frontal diameter. – The circumference of the head.
    • 82. Cephalopelvic Disproprtion • CPD is obstructed labor resulting from disparity between the size of the fetal head and maternal pelvis. – E.g. small pelvis, nongynecoid pelvis, large fetus, or more commonly a combination of these factors. – True CPD is rare, 1 in 250 pregnancies or 0.4% of the time • Failure to progress : lack of progressive cervical dilatation or lack of fetal descent. – Mostly due to asynclitism, malpresentation or ineffective uterine contractions.
    • 83. • Diagnosis: – Research indicates that pelvimetry is not a useful diagnostic tool for CPD. – Unless there’s obvious abnormal pelvis a ‘trial of labor’ is the only true way to diagnose CPD difficult to anticipate how well the fetal head and the maternal pelvis will adjust & mould to each other. – Squatting will open up the pelvis at least 33% more.
    • 84. • Treatment of CPD: –If the surgeon is absolutely certain that there is CPD, then a CS is the only option for delivery. –But if diagnosis is doubtful a ‘trial of labour’ should always be offered • If, after sufficient time symptoms of prolonged labor or fetal distress begins to develop, a CS needs to be carried out.

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