6. Anatomy of the Female Pelvis and Fetal Skull
Study Session 6 Anatomy of the Female Pelvis and Fetal Skull 3
Learning Outcomes for Study Session 6 3
6.1 The female bony pelvis 3
6.1.1 Ilium 4
6.1.2 Ischium 5
6.1.3 Pubic bones and the symphysis pubis 5
6.1.4 Sacrum 5
6.2 The pelvic canal 5
6.2.1 The size and shape of the pelvis 6
6.2.2 The pelvic inlet 7
6.2.3 The pelvic outlet 7
6.3 The fetal skull 9
6.3.1 Fetal skull bones 9
6.3.2 Sutures 10
6.3.3 Fontanels 12
6.3.4 Regions and landmarks in the fetal skull 12
Summary of Study Session 6 13
Self-Assessment Questions (SAQs) for Study Session 6 13
SAQ 6.1 (tests Learning Outcomes 6.1, 6.2 and 6.3) 13
Matching quiz 13
SAQ 6.2 (tests Learning Outcomes 6.1, 6.2 and 6.3) 15
SAQ 6.3 (tests Learning Outcomes 6.1, 6.2 and 6.3) 16
Study Session 6 Anatomy of the Female Pelvis and Fetal Skull
In this study session you will learn about the bony structures with the most importance for the pregnant woman and the baby she will give birth to. The bones of the skeleton have the main function of supporting our body weight and acting as attachment points for our muscles. The focus in this study session will be on the female pelvis, which supports the major load of the pregnant uterus, and the fetal skull, which has to pass through the woman’s pelvis when she gives birth.
There are certain key landmarks in the anatomy of the female pelvis and the fetal skull that we will show you in this study session. Knowing these landmarks will enable you to estimate the progress of labour, by identifying changes in their relative positions as the baby passes down the birth canal. You will learn how to do this in the next Module in this curriculum, which is on Labour and Delivery Care.
Learning Outcomes for Study Session 6
When you have studied this session, you should be able to:
6.1 Define and use correctly all of the key words printed in bold.
(SAQs 6.1, 6.2 and 6.3)
6.2 Describe the female pelvis and identify the important features for obstetric care. (SAQs 6.1, 6.2 and 6.3)
6.3 Describe the main features of the fetal skull, and their importance for labour and delivery. (SAQs 6.1, 6.2 and 6.3)
6.1 The female bony pelvis
The pelvis is a hard ring of bone (see Figure 6.1), which supports and protects the pelvic organs and the contents of the abdominal cavity. The muscles of the legs, back and abdomen are attached to the pelvis, and their strength and power keep the body upright and enable it to bend and twist at the waist, and to walk and run.
Figure 6.1 The bones of the female pelvis.
The woman’s pelvis is adapted for child bearing, and is a wider and flatter shape than the male pelvis. The pelvis is composed of pairs of bones, which are fused together so tightly that the joints are difficult to see. We will describe each of the bones in turn, and their major landmarks. It will help you to visualise the anatomy of the pelvis if you keep referring back to Figure 6.1.
Ilium is pronounced ‘ill ee umm’ and iliac is ‘ill ee ack’.
The major portion of the pelvis is composed of two bones, each called the ilium — one on either side of the backbone (or spinal column) and curving towards the front of the body. When you place your hand on either hip, your hand rests on the iliac crest, which is the upper border of the ilium on that side. At the front of the iliac crest, you can feel the bony protuberance called the anterior superior iliac spine (a ‘protuberance’ is something that sticks out, like a little hill or knob).
What do the directional terms ‘anterior superior’ tell you about the position of the iliac spines? (If you can’t remember, look back at Box 3.1 in Study Session 3.)
Anterior tells you that the iliac spines are at the front of the body, and superior tells you that they are above the main portion of the ilium on each side.
End of answer
The ischium is the thick lower part of the pelvis, formed from two fused bones — one on either side. When a woman is in labour, the descent of the fetal head as it moves down the birth canal is estimated in relation to the ischial spines, which are inward projections of the ischium on each side. The ischial spines are smaller and rounder in shape in the woman’s pelvis than in that of the man. In the Module on Labour and Delivery Care, you will learn how to feel for the ischial spines to help you estimate how far down the birth canal the baby’s head has progressed.
Ischium is pronounced ‘iss kee umm’ and ischial is ‘iss kee al’.
The pubic bones on either side form the front part of the pelvis. The two pubic bones meet in the middle at the pubic symphysis. (A symphysis is a very strong bony joint.) The pubic symphysis is immediately below the hair-covered pubic mound that protects the woman’s external genitalia (as shown in Figure 3.2, if you want to look back at it now).
When you examine the abdomen of a pregnant woman, feeling for the top of the pubic symphysis with your fingers is a very important landmark. In Study Session 10, you will learn how to measure the height of the uterus from the pubic symphysis to the fundus (top of the uterus — see Figure 3.3 if you need to remind yourself of the position of the fundus). This measurement enables you to estimate the gestational age of the fetus, i.e. how many weeks of the pregnancy have passed, and whether the fetus is growing at the normal rate.
Sacrum is pronounced ‘say krum’. Coccyx is pronounced ‘kok six’.
The sacrum is a tapered, wedge-shaped bone at the back of the pelvis, consisting of five fused vertebrae (the small bones that make up the spinal column or backbone). At the bottom of the sacrum is a tail-like bony projection called the coccyx. The upper border of the first vertebra in the sacrum sticks out, and points towards the front of the body; this protuberance is the sacral promontory — an important landmark for labour and delivery.