Repro: The Pelvis As A Birth Canal

Question 1

What are the features of a gynecoid pelvis?

Answer 1

• round inlet
• straight side walls
• ischial spines not too prominent
• well rounded greater sciatic notch
• well curved sacrum
• subpubic arch >90 degrees

Question 2

What is the ‘true’ and ‘false’ pelvis?

Answer 2

The false pelvis is the structures above the lines terminalis eg the ala

• called the greater pelvis
• has no obstetric relevance

The true pelvis is the structures below the linea terminalis

• called the lesser pelvis
• has an immobile solid bony canal

Question 3

How do you make a clinical assessment of the pelvic inlet?

Answer 3

The true measure is the obstetric conjugate:
Measured from the sacral promontory to the midpoint of the pubic symphysis.

However you cannot get to the midpoint of the pubic symphysis so have to use the diagonal conjugate:
Measured from the sacral promontory to the inferior border of the pubic symphysis. (Usually marginally bigger)

Question 4

What is the bispinous diameter?

Answer 4

The distance between the 2 ischial spines - want it to be as wide as possible

Question 5

What are the 2 borders of the pelvic outlet composed of?

Answer 5

The anterior border is bony therefore immobile

The posterior is a ligament border - high progesterone and relaxin during pregnancy soften the soft tissues and ligaments so they have more give