The Female Pelvis

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Anatomy of the female pelvis

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Functions of the female pelvis

Functions of the female pelvis

  •  Supports upper body 
  •  Transmits weight to lower limbs 
  • Enables movement
  • takes weight of body when sitting on ischial tuberosities 
  •  protects reproductive organs, bladder & rectum 
  • In pregnancy - supports the gravid uterus 
  • Essential in mechanism of birth 
  • Sacrum allows for distribution of nerves to the pelvis
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The true pelvis and the false pelvis

The True Pelvis

Separated from the false pelvis by the brim. 

  • Consists of 3 regions – brim, cavity & outlet 
  •  Fetus negotiates each simultaneously 
  • Fetus follows plane of brim & cavity to ischial spines 

The False Pelvis 

  • The pelvic brim divides the two parts true and false 
  • The false pelvis being located above the pelvic brim 
  • It has no obstetric significance
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The Pelvic Cavity

Pelvic cavity 

  • Extends downwards from the brim 
  • Wedge shaped –shallow at front & deep at back 
  • Viewed from above it is circular shaped 
  • Designed to facilitate the descent & rotation of the presenting part of fetus
  • Boundaries include – curve of sacrum, sacroiliac joints, ischia, superior & inferior pubic ramus & pubis 
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The Pelvic Outlet

Pelvic outlet

  • Diamond shaped
  • Can be described as an anatomical structure & by its obstetric dimension ie it space value
  • Boundaries include- tip of coccyx, ischial tuberosities & pubic arch
  • Obstetric boundaries – inner aspect of sacral base,ischial spines, lower inner border of symphysis pubis & sacrospinous ligaments 
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Diameters of the pelvis

                Anterior/posterior                              Oblique                           Transverse


Brim              11CM                                          12CM                               13CM


Cavity            12CM                                          12CM                               12CM


Outlet            13CM                                          12CM                               11CM

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Bone of the pelvis

Consists of 4 pelvic bones

X 2 innominate bones each side consisting of 3 parts:

  • ilium
  • ischium
  • pubic bone

+ X1 sacrum

+ X1 coccyx 

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The Gynaecoid Pelvis

Gynaecoid Pelvis

  • Round brim
  • Curved sacrum 
  • Blunt spines
  • Pubic angle 90 degrees small to normal sized women
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The Android Pelvis

Android pelvis

  • Heart shaped brim
  • Straight sacrum
  • Prominent spines
  • Pubic arch less than 90 degrees
  • Favours OP position (Occiput posterior)
  • And women of short stature & from african descent
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The Anthropoid Pelvis

Anthropoid pelvis

  • Oval shaped
  • Spines not prominent
  • Pubic angle wide
  • Favours tall women (engaging position usually continues through pelvis)
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The Platypelloid Pelvis

Platypelloid pelvis 

  • Kidney shaped
  • Sacrum flat
  • Blunt spines
  • Wide pubic arch
  • Fetus can enter but can’t go through outlet
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The Pelvic Joints

Pelvic joints

  • Sacroiliac joint is where ilium meets with 1st 2 sacral vertebrae 
  • Symphysis pubis between 2 pubic bones
  • Sacrococcygeal joint between sacrum & coccyx
  • Lumbar sacral joint which articulates with the lumbar vertebrae 

All are supported by Sacroiliac ligaments

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The Pelvic Planes

Pelvic planes

There are 3 common planes of the pelvis:

  • The pelvic brim
  • Mid cavity
  • Outlet

A pelvis with an adequate brim and cavity rarely if ever has reduced diameters of the outlet

The coccyx has mobility which also aids available space

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Increasing the diameter of the pelvis

Increasing the diameter

  • Russell’s research studied pelvic X rays of 69 women in 1969 in 3rd trimester
  • The women were in dorsal (lying down) and sitting positions
  • As much as 28% increase in the pelvic outlet is possible (i.e 1cm in transverse & 2cm in AP diameter , if alternative positions are adopted.

Upright or squatting is ideal

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Key Points

Points to note

  • Pelvic measurements may widen during labour due to pelvic ligament laxity
  • The position of the mother in labour also affects the pelvic outlet diameter
  • Moulding may reduce the absolute measurements of the fetal skull during labour
  • The degree of flexion of the fetal skull at the neck (attitude) determines the diameter of the fetal skull presenting to the pelvis
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