Female Bony Pelvis & Fetal Head

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• Bony pelvis and fetal skull
• Dr Malleswar Rao K

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Objects

• Fetal head
• Pelvic anatomy
• Pelvic shapes

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Passenger
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Fetal head

• Landmarks
• Sutures
• Fontanelles
• Diameters

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Fetal head

• From an obstetrical point of view its the most
  important part
• largest
• least compressible part of the fetus.
• most frequent presenting part

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Landmarks

• Head is divided into 3areas
• (1) the sinciput or brow portion
• (2) the vertex, or top of the head between the 2
  fontanelles
• (3) Base large, ossified, firmly united, and
  noncompressible

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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

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• 2-lambdoid suture
• extends from the posterior fontanelle laterally
• separate the occipital from the parietal bones.

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• 3-coronal suture
• extends from the anterior fontanelle laterally
• separate the parietal and frontal bones.

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• 4- frontal suture
• lies between the frontal bones
• extends from the anterior fontanelle to the
  glabella (the prominence between the eyebrows).

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Clinical importance of sutures

• 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.

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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.

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

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• The anterior fontanelle (bregma)
• diamond shaped area(2 3 cm) of unossified
  membrane formed by the junction of 4 suture.

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• The posterior fontanelle
• It is the triangular depressed area at the
  junction of 3 suture
• closes at 6 to 8 weeks of life
• Y- or T-shaped

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ROT
LOT
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LOA
ROA
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LOP
ROP
LOP
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Transverse Diameters of the Fetal Skull
Biparietal Diameter 9.5 cm Between the 2 parietal eminences
Bitemporal Diameter 8.5 cm.
Bimastoid Diameter 7.5 cm. Between the 2 mastoid processes (Not reducible nor destroyable even by destructive procedures
Supra-subparietal 8.25 - 9 cm. Asynclitic head
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• presenting AP diameter when the head is deflexed
  gtgtgt OP

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• presenting AP diameter in a brow presentation
• longest AP diameter of the head

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-4. Submentobregmatic (9.5 cm)presenting AP
diameter in face presentations
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Length Presentation
1-Suboccipito-bregmatic 9.5 cm. Flexed vertex
2-Suboccipito-frontal 10.5 cm. Partially deflexed vertex
3-Occipito-frontal 11.5 cm. Deflexed vertex
4-Mento-vertical 13.75-14 cm. Brow
5-Submento-bregmatic 9.5 cm. Face
6-Submento-vertical 11.5 cm. Face Not fully extended
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Engaging Diameters of Fetal Skull
Well Flexed Head Circle of 9.5 cm. The engaging Diameter is the Suboccipito-Bregmatic diameter
A deflexed Head An oval The longer occipito-frontal diameter Of 11.5 cm. Is exposed.
Greater Deflexion of the Head An oval The longer mento vertical diameter of 13.75-14 cm. is exposed
Full Extension of the Head A circle of 9.5 cm. The engaging dimeter is the submento-vertical diameter
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Female bony pelvis
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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.

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Pelvic outlet
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SP
Ischial Spine
Ischial Tuberosity
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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

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(Inlet (Pelvic brim)
Bounded by
passing with the boundaries of pelvic brim and
making an angle of 55o with the horizon (angle of
pelvic inclination).
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Pelvic inclination The plane of the pelvic
inlet makes an angle of 55 degree with the
horizon in the standing position"
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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.

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Diameters of the pelvic inlet
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(4) External conjugate From The upper anterior
margin of the symphysis pubis. To The depression
below the tip of the 5th lumbar spine (20 cm).
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(5) Anatomical transverse diameter Between the
farthest points on iliopectineal lines ( 13
cm). It lies 4 cm infornt of the sacral
promontory, 7 cm behind the symphysis pubis.
(6) Obstetric transverse diameter It bisects the
true conjugate (12.5 cm)
TC
ATD
OTD
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(7) The oblique diameters (12 cm) The right
extends from the right joint to the left eminence
and vice versa.
(8) Sacrocotyloid diameter (9-9.5 cm) The right
diameter ends in the right eminence vice versa.
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The pelvic Cavity

• Boundaries
• Above pelvic brim.
• Below plane of least pelvic dimensions.
• Anteriorly syrnphysis pubis.
• Posteriorly sacrum.

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2- pelvic cavity The plane of greatest diameter

• 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

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The pelvic Outlet

• Anatomical outlet Lozenge -shaped, bounded by
• Lower border of symphysis pubis.
• Pubic arch.
• Ischial tuberosities
• Sacrotuberous sacrospinous ligaments.
• Tip of the coccyx.

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The Plane of the Outlet
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Diameters of the pelvic outlet

• Anteroposterior
• Anatomical anteroposterior (11 cm)
• b Obstetric anteroposterior (13 cm)

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Diameters of the pelvic outlet
(2) Transverse diameters Bituberous (11 cm),
between the inner aspects of ischial
tuberosities Bispinous (10.5 cm), between the
tips of ischial spines.
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Diameters of the pelvic outlet
(3) Anterior sagittal diameter 6-7 cm . (4)
Posterior sagittal diameter 7-10 cm
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Diameters of the pelvic
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The pelvic axis Anatomical axis (Curve of
Carus)
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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

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The Fetal Head Has Five Fifths
fifth above the pelvic brim
0 Head Not Palpable 1 Sinciput felt Occiput
Not Felt 2 Sinciput felt Occiput Just Felt 3
Sinciput easily felt Occiput Felt 4
Sinciput High Occiput easily Felt 5 Complete
above pelvic brim
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Pelvic Shapes
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Gynecoid Pelvis

• The classic female type.
• Found in approximately 50 of women.
• Characteristics

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Android Pelvis

• The typical male type
• Found in less than 30 of women
• Characteristics
• Triangular inlet with a flat

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Anthropoid Pelvis

• Resembles ape pelvis.
• Found in approximately 20 of women
• Characteristics
• ,

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Platypelloid Pelvis

• Flattened gynecoid pelvis.
• Found in only 3 of women

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