Anatomy of the female pelvis and vaginal birth

Anatomy of the female pelvis and vaginal birth © Royal College of Obstetricians and Gynaecologists

Take a look at the bony pelvis you have been given. View it from the front. In the following slides, the bony landmarks will be described. © Royal College of Obstetricians and Gynaecologists

Innominate bone © Royal College of Obstetricians and Gynaecologists

Sacrum © Royal College of Obstetricians and Gynaecologists

Coccyx © Royal College of Obstetricians and Gynaecologists

Sacroiliac joint © Royal College of Obstetricians and Gynaecologists

Sacrococcygeal joint © Royal College of Obstetricians and Gynaecologists

Symphysis pubis © Royal College of Obstetricians and Gynaecologists

Ischial spine © Royal College of Obstetricians and Gynaecologists

Ileopectineal line © Royal College of Obstetricians and Gynaecologists

Obturator foramen © Royal College of Obstetricians and Gynaecologists

Pubic arch © Royal College of Obstetricians and Gynaecologists

Sacral promontory © Royal College of Obstetricians and Gynaecologists

Anterior foramina © Royal College of Obstetricians and Gynaecologists

Now look at the pelvis from one side. In the following slides, more landmarks will be shown. You will also see how the pelvis is orientated when a woman is standing up straight. © Royal College of Obstetricians and Gynaecologists

Anterior superior iliac spine Symphysis pubis Vertical plane © Royal College of Obstetricians and Gynaecologists

Ileum Pubis Ischium © Royal College of Obstetricians and Gynaecologists

Acetabulum Obturator foramen © Royal College of Obstetricians and Gynaecologists

Look at the pelvis from the front again. In the following slides, you will be shown a little more anatomy. Look at the position of the sacrotuberous and sacrospinous ligaments. © Royal College of Obstetricians and Gynaecologists

Sacrotuberous ligament © Royal College of Obstetricians and Gynaecologists

Sacrospinous ligament © Royal College of Obstetricians and Gynaecologists

Look at the pelvis from behind. Look at the position of the sacrotuberous and sacrospinous ligaments. These delineate the greater and lesser sciatic foraminae. © Royal College of Obstetricians and Gynaecologists

Sacrospinous ligament © Royal College of Obstetricians and Gynaecologists

Sacrotuberous ligament © Royal College of Obstetricians and Gynaecologists

Greater sciatic foramen Lesser sciatic foramen © Royal College of Obstetricians and Gynaecologists

We are now going to add in some muscles. You will see piriformis from front and back. You will see obturator internus from the back. © Royal College of Obstetricians and Gynaecologists

Piriformis © Royal College of Obstetricians and Gynaecologists

Obturator internus © Royal College of Obstetricians and Gynaecologists

We are now going to add in blood vessels and nerves. Look at the pelvis from the front again. © Royal College of Obstetricians and Gynaecologists

Common Iliac A Internal Iliac A © Royal College of Obstetricians and Gynaecologists

External Iliac A © Royal College of Obstetricians and Gynaecologists

Common Iliac V Internal Iliac V © Royal College of Obstetricians and Gynaecologists

The Lumbosacral Plexus © Royal College of Obstetricians and Gynaecologists

Sciatic nerve © Royal College of Obstetricians and Gynaecologists

Pudendal nerve © Royal College of Obstetricians and Gynaecologists

Obturator nerve © Royal College of Obstetricians and Gynaecologists

Look at the pelvis from the side. We will look at the muscles and ligaments on the side wall of the pelvis. You will see where the levator ani muscles originate. You will also see the critical dimensions of the pelvis. © Royal College of Obstetricians and Gynaecologists

Sacrotuberous ligament © Royal College of Obstetricians and Gynaecologists

Sacrospinous ligament © Royal College of Obstetricians and Gynaecologists

Obturator canal © Royal College of Obstetricians and Gynaecologists

Obturator internus Muscle Covered by Fascia © Royal College of Obstetricians and Gynaecologists

Pudendal canal © Royal College of Obstetricians and Gynaecologists

Line of attachment of levator ani © Royal College of Obstetricians and Gynaecologists

Critical pelvic dimensions Pelvic inlet © Royal College of Obstetricians and Gynaecologists

Critical pelvic dimensions Pelvic midplane © Royal College of Obstetricians and Gynaecologists

Critical pelvic dimensions Pelvic outlet © Royal College of Obstetricians and Gynaecologists

Female Male Pelvic inlet Pelvic outlet Pelvic cavity Pubic arch © Royal College of Obstetricians and Gynaecologists

Look at the pelvis from the front again. Imagine a ‘coronal’ plane through the middle of the pelvis. You will see the rectum coming through the pelvis. You will see where the levator ani muscles originate. You will see which structures form the pelvic diaphragm. © Royal College of Obstetricians and Gynaecologists

Iliac crest Pelvic brim Ischial tuberosity © Royal College of Obstetricians and Gynaecologists

Rectum © Royal College of Obstetricians and Gynaecologists

Obturator Internus With Fascia © Royal College of Obstetricians and Gynaecologists

Levator ani Plus coccygeus Makes Pelvic diaphragm © Royal College of Obstetricians and Gynaecologists

There are some structures above the pelvic diaphragm. There are some structures below the pelvic diaphragm. © Royal College of Obstetricians and Gynaecologists

Peritoneum © Royal College of Obstetricians and Gynaecologists

Subperitoneal space © Royal College of Obstetricians and Gynaecologists

Contains: Pubocervical Trans cervical Sacrocervical Ligaments © Royal College of Obstetricians and Gynaecologists

Perineum everything under pelvic diaphragm © Royal College of Obstetricians and Gynaecologists

Ischiorectal fossae © Royal College of Obstetricians and Gynaecologists

Now look at the pelvis from below. Look at the layout of the bones and the ligaments. They define the pelvic outlet. © Royal College of Obstetricians and Gynaecologists

Obturator membrane Obturator canal © Royal College of Obstetricians and Gynaecologists

Pubic arch Symphysis pubis Inferior pubic ramus Ischial ramus © Royal College of Obstetricians and Gynaecologists

Sacrotuberous ligament Ischial tuberosity Sacrum / coccyx © Royal College of Obstetricians and Gynaecologists

Pelvic outlet © Royal College of Obstetricians and Gynaecologists

Urogenital triangle Anal triangle © Royal College of Obstetricians and Gynaecologists

Keep looking at the pelvis from below. Imagine the anatomy above the pelvic diaphragm. The following slides show the structures encountered as you descend through the pelvis. © Royal College of Obstetricians and Gynaecologists

Bladder Above the Cervix Pelvic diaphragm Rectum © Royal College of Obstetricians and Gynaecologists

Pubocervical ligament Above the Pelvic diaphragm © Royal College of Obstetricians and Gynaecologists

Above the Pelvic diaphragm Transverse cervical ligament © Royal College of Obstetricians and Gynaecologists

Above the Pelvic diaphragm Sacrocervical ligament © Royal College of Obstetricians and Gynaecologists

Pelvic diaphragm Levator ani: Pubococcygeus Iliococcygeus Ischiococcygeus Coccygeus © Royal College of Obstetricians and Gynaecologists

Keep looking at the pelvis from below. Imagine the anatomy as you descend below the pelvic diaphragm. The following slides show the structures encountered as you continue to descend through the pelvis. © Royal College of Obstetricians and Gynaecologists

Urogenital diaphragm Superior layer of fascia © Royal College of Obstetricians and Gynaecologists

Urogenital diaphragm Sphincter urethrae Deep transverse peroneal muscles © Royal College of Obstetricians and Gynaecologists

Perineal membrane © Royal College of Obstetricians and Gynaecologists

Structures in Superficial pouch Clitoris & crus Bulb of vestibule Vestibular glands © Royal College of Obstetricians and Gynaecologists

Muscles in Superficial pouch Ischiocavernosus Bulbospongiosus Supl transverse peroneal muscles © Royal College of Obstetricians and Gynaecologists

Perineal body © Royal College of Obstetricians and Gynaecologists

Keep looking at the pelvis from below. You have now reached the most superficial level. © Royal College of Obstetricians and Gynaecologists

Labium majus Labium minus © Royal College of Obstetricians and Gynaecologists

Mons pubis Prepuce of clitoris Vestibule vagina Fourchette © Royal College of Obstetricians and

Here is the female abdomen and pelvis viewed from one side. The structures shown should now be familiar to you. © Royal College of Obstetricians and Gynaecologists

Sacrocervical ligament Pubocervical ligament © Royal College of Obstetricians and Gynaecologists

Pelvic diaphragm © Royal College of Obstetricians and Gynaecologists

Urogenital diaphragm © Royal College of Obstetricians and Gynaecologists

Here is the rectum. Look at its anatomical relations. © Royal College of Obstetricians

Rectum Sacrum Perineal body Anococcygeal body © Royal College of Obstetricians and Gynaecologists

Puborectalis Deep Superficial Subcutaneous © Royal College of Obstetricians and Gynaecologists

Take your fetal skull and view it from above. Note the near central position of the anterior fontanelle. © Royal College of Obstetricians and Gynaecologists

parietal eminence coronal sutures frontal bones lambdoid sutures occiput anterior fontanelle saggital suture posterior fontanelle © Royal College of Obstetricians and Gynaecologists

The following slides will demonstrate the orientation of the fetal skull as it passes through the pelvis in normal labour. © Royal College of Obstetricians and Gynaecologists

passenger the head flexes as the uterus contracts the head descends and engages in the pelvis the leading part approaches the ischial spines © Royal College of Obstetricians and Gynaecologists

passenger the occiput starts to rotate anteriorly the occiput reaches the pelvic floor (levator ani) internal rotation continues to achieve an occipito-anterior position © Royal College of Obstetricians and Gynaecologists

passenger the occiput clears the symphysis pubis the head extends to deliver © Royal College of Obstetricians and Gynaecologists

passenger the head sits on the maternal perineum © Royal College of Obstetricians and

passenger the fetal head realigns itself with the fetal shoulders - restitution © Royal College of Obstetricians and Gynaecologists

passenger the shoulders contact the pelvic floor and rotate so that the bisacromial diameter lies in an anteroposterior orientation the head therefore continues to rotate - external rotation © Royal College of Obstetricians and Gynaecologists