OBSTETRIC ANATOMY Flashcards
(23 cards)
outline the The Caldwell-Moloy’s classification of female pelvis
They differ in:
Shape of the pelvic inlet
Shape of the side-walls
Character of the subpubic arch
Four types do exist:
Gynecoid: 50%. female. Inlet: Rounded. Cavity: Wide and shallow. Subpubic angle: >90. Ischial Spines: Not prominent
Android: 20%. male like. Triang. Narrow and deep. <70. Inward projection
Anthropoid: 25%. ape like. AP-oval. Wide. <90. Prominent
Platypelloid: 5%. flat. Trans-oval. Wide. >90. Not prominent
Walls Parallel Convergen t Parallel Divergent
differentiate between true and false pelvis
False pelvis: above the pelvic brim and has no obstetric importance. True pelvis: below the pelvic brim. It is the bone defined tunnel that the infant must traverse at birth.
these 2 are divided by ileopectineal line
explain the of the Planes of the pelvis?
- Plane of the pelvic inlet - passing with the boundaries of pelvic brim and making an angle of 55o with the horizon (angle of pelvic inclination).
- Plane of the cavity: Plane of greatest Pelvic Dimensions. It passes between the middle of the posterior surface of the symphysis pubis and the junction between 2nd and 3rd sacral vertebrae. Laterally, it passes to the centre of the acetabulum and the upper part of the greater sciatic notch. It is a round plane with diameter of 12.5 cm. Internal rotation of the head occurs when the biparietal diameter occupies this wide pelvic plane while the occiput is on the pelvic floor i.e. at the plane of the least pelvic dimensions.
- Plane of the mid pelvis (plane of obstetric outlet) - It is the plane of least pelvic dimensions. It passes from the lower border of the symphysis pubis anteriorly, to the ischial spines laterally, to the tip of the sacrum posteriorly. It is the plane of the pelvic floor. The head is considered engaged if the vault reaches it. This is the plane where the pelvic axis turns forwards.
- Plane of the Anatomical outlet - It passes with the boundaries of anatomical outlet and consists of 2 triangular planes with one base which is the bituberous diameter. Anterior sagittal plane: its apex at the lower border of the symphysis pubis. Anterior sagittal diameter from the lower border of the symphsis pubis to the centre of the bituberous diameter: 6-7 cm Posterior sagittal plane: its apex at the tip of the coccyx. Posterior sagittal diameter from the tip of the sacrum to the centre of the bituberous diameter: 7.5-10 cm
describe The Ideal Obstetric Pelvis
Brim: Round or Oval transversely No undue projection of sacral promontory. AP diameter: 12 cm. Transverse diameter: 13 cm The plane of pelvic inlet not more than 55°.
Cavity: Shallow with straight side-walls. No great projections of ischial spines. Smooth sacral curve
Outlet: Pubic arch rounded Subpubic angle >80°. Intertuberous diameter of at least 10 cm.
describe The formation of the lower uterine segment
It is the part between the vesico-uterine fold of peritoneum superiorly and the cervix inferiorly. It develops as early as the 16th week by incorporating the upper part of the cervix in the lower part of the uterus to accommodate for the presenting part of the fetus.
describe the Formation of the Birth Canal During Labor
The lower uterine segment, cervix and vagina become a single canal that allow for the passage of the baby to the outside. Hypertrophy of the vaginal muscle layer and unfolding of the rugae allow for the accommodation of the fetus without damage.
The cervix is obliterated, taken-up or effaced: It is reduced from a length of 2-2.5 cm to a mere paper thin circular orifice.
what is fetal presentation and presenting part?
Fetal Presentation: Is the fetal pole that presents at the pelvic inlet:
Cephalic: Head First
Breech: Feet or Buttocks
Shoulder: back or abdomen
The Presenting part: Is the part of the fetus first touched by the examining fingers during pelvic examination.
what is Fetal Lie
Refers to the relationship between the fetal longitudinal axis and that of the mother.
what is position?
It refers to the relationships of a designated point on the presenting part “Denominator” to the walls of maternal pelvis.
outline the suboccipito-bregmatic diameter occupation in succession as the fetal head descends
As the fetal head descends through the birth canal, the suboccipito-bregmatic diameter successively occupies the :
Transverse diameter of the inlet.
Oblique diameter of the cavity.
AP diameter of the outlet
What is the predominant fetal head position?
During labor, in 90% of vertex presentation, The head assumes either a LOA or a ROP position The sagittal suture occupies the Right Oblique diameter of the pelvis. The right oblique diameter of the pelvis goes from the left iliopectineal eminence to the Right sacroiliac joint.
what isThe Stations of the Fetal Head?
The location of the presenting part with reference to the ischial spine is designated the station of the presenting part.
The head is said to be engaged when the vertex is felt at the level of the ischial spine. In that instance, the biparietal diameter should have negotiated the inlet. This is because: The distance from the plane of the inlet to the spine is 5 cm. The distance from the vertex to the biparietal diameter is 4.5 or less
outline the 5ths of the fetal head
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
outline the anatomy of the body of the uterus
29.The body of the uterus: It has three layers: The endometrium, the myometrium and the perimetrium: The myometrium: Has longitudinal, circular and oblique muscle fibers and is very expansile. The oblique muscle fibers run “criss-cross” and compress the blood vessels when the uterus is well contracted. It is found mostly in the upper segment of the uterus, where the placenta normally embeds. The richness in muscle fibers and its criss-cross important to ensure proper hemostasis following placental delivery. In contrast to that is the lower uterine segment which is poor hemostasis following placental delivery. This explains why bleeding in the third stage is more difficult to control if the placenta is implanted in the lower uterine segment as in cases of placenta praevia. The Endometrium: During pregnancy and childbirth, the endometrium is referred to as the decidua. The perimetrium: Is a layer of peritoneum that covers the uterus except at the sides where It extends to form the broad ligaments. Significant bleeding and hematoma can extend whithin the layers of the broad ligament into the extra peritoneal space with serious consequences
outline the anatomy of the cervix
30.The Cervix: Consists predominantly of collagenous connective tissue and mucopolysaccaride ground substance. It communicates with the uterine cavity through the internal os and with the vaginal canal through the external os. The endocervical canal is about 2.5 to 3 cm in length. It is lined by a single layer of specialized columnar epithelium and secretes mucus to facilitate sperm transport. During pregnancy the glands secretion forms a plug of mucus which helps protect against infection. This plug of mucous comes away stained with some blood just before labor commences. Many women refer to this as the “show”.
what are the 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
what is 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.
Overmoulding
Occurs in case of obstructed labor. There is overstretch of the falx cerebri which tears from its attachment at the tentorium cerebelli. Subsequently there is injury of the vein of Galen with ICH.
list the Scalp Tissues layers
There are Five layers of scalp tissue
Skin: The outer covering containing hair.
Subcutaneous tissue Muscle Layer: containing the tendon of Galae.
Connective tissue: a loose layer.
Periosteum: covers the skull bones and attached at the suture line
what is Caput Succedaneum?
Oedema of scalp due to venous & lymphatic obstruction resulting from prolonged pressure by cervix & bony pelvis.
Swelling is formed due to stagnation of fluid in scalp layers beneath the girdle of contact interfering with venous
return & lymphatic drainage from unsupported area of scalp → stagnation of fluid
and appearance of a swelling in the scalp.
Oedema is above the periosteum, present at birth and decrease in size.
“Pits” on pressure, crosses a suture lines.
Usually resolves within 36 hours
May be caused by the cup of ventouse – chignon
Can be confused with cephalhematoma
Significance – signifies static position of the head for a long period of time
Labour was difficult& prolonged.
Its position indicates the head position (formed over lowest part of the head) and degree of flexion achieve
Diffuse scalp edema resulting from venous congestion due to prolonged pressure on the fetal head by the pelvic bones. It is soft and boggy to touch It usually disappears Localized caput…? It is usually few mm. Thick but may be large and lead to misinterpretation of the station of the head. The presence of caput may have medico-legal implication: The baby was living Labor was difficult D.D…Cephalhematoma
what is Cephalhematoma?
This swelling is due to bleeding between the skull bone and periosteum. Bleeding occurs due to friction between the overriding bones and periosteum during molding. It is just as likely to occur during a normal delivery as during more difficult labor. A low prothrombin level is probably a contributory cause
Cephalhematoma is not present at birth but appears 2-3 days. The swelling is limited by the periosteum. It therefore can NOT lie over a suture. The head is more red ad bruised in appearance than in caput succedaneum. The swelling may increase and it takes 6 weeks at least to disappear.
Describe the perineum
Perineum
Final obstacle negotiated by fetus during labour is perineum.
Perineal body is a condensation of fibrous and muscular tissue lying
betwn vagina and the anus.
Receives attachments of posterior ends of bulbo-cavernous muscles,
medial ends of superficial & deep transverse perineal muscles, and
anterior fibres of the external anal sphincter
Obstetrical perineum: (Synonyms: Perineal body), its pyramidal shaped tissue where pelvic floor and perineal
muscles and fascia meet in between the vagina and the anal canal and measures about 4 cm × 4 cm with the base
covered by perineal skin and the apex is pointed and is continuous with rectovaginal septum
Grades of moulding
There are 3 gradings; Principle of moulding of head
a) Grade 1 : Approximation of skull bones (bones touching but not overlapping)
b) Grade 2: Overriding of bones but reducible (easily separated)
c) Grade 3: Irreducible overriding of skull bones, sign of obstructed labour & may lead to intracranial hemorrhage
