56. Anatomy of the bony female pelvis and the fetal skull

Question 1

common pelvic shapes

Answer 1

1. Gynecoid (50%)
2. Android (30%)
3. Anthropoid (25%)
   4.Platypelloid (rare<3%)

Question 2

describe a Gynecoid pelvis

Answer 2

round inlet, sidewalls are straight, ischial spines are not prominent (diameter >10cm)
good prognosis for vaginal delivery

Question 3

describe a Android pelvis

Answer 3

heart-shaped, sidewalls are convergent, prominent ischial spines (diameter <10cm), sacrum is forward and straight with little curvature
Limited posterior space for fetal head → poor prognosis for vaginal delivery

Question 4

describe Anthropoid shape of the pelvis

Answer 4

vertically oriented oval, sidewalls are convergent, prominent ischial spines (diameter <10cm), sacrum is straight= pelvis is deeper than other types
Good prognosis for vaginal delivery;
commonly seen with OP position

Question 5

describe Platypelloid shape of pelvis

Answer 5

Horizontally oriented oval inlet, sidewalls are divergent than convergent, ischial spines are not prominent (diameter >10cm), sacrum is well curved and rotated backward, short, shallow pelvis
poor prognosis for vaginal delivery

Question 6

what 4 bones make up the bony pelvis?

Answer 6

the sacrum (5 fused vertebrae), coccyx, and 2 innominates (composed of the ilium, ischium, and pubis)

Question 7

The anterior superior edge of the 1st sacral vertebra is called ?

Answer 7

promontory, which protrudes slightly into the cavity of the pelvis

Question 8

The pelvis is divided into

Answer 8

the false pelvis above and the true pelvis below the linea terminalis

Question 9

The only obstetric function of the false pelvis?

Answer 9

is to support the pregnant uterus

Question 10

how is The true pelvis formed?

Answer 10

by the sacrum and coccyx posteriorly and by the ischium and pubis laterally and anteriorly

Question 11

what 4 imaginary planes is the pelvis divided into?

Answer 11

•The pelvic inlet: the entry of the fetal head
•The plane of greatest diameter: where the fetal head rotates to the anterior position
•The plane of least diameter: the most important because most instances of arrest of descent occurs at this level
•The pelvic outlet

Question 12

The fetal skull consists of ?

Answer 12

a base and a vault (the cranium)

Question 13

structure of the base

Answer 13

large, ossified, firmly united, and noncompressible bones serving to protect the vital structures within the brain stem and its spinal connections

Question 14

the cranium consists of?

Answer 14

the occipital bone posteriorly, 2 parietal bones laterally, and 2 frontal and temporal bones anteriorly

Question 15

what are the structure of the cranial bones at birth?

Answer 15

thin, weakly ossified, easily compressible, and interconnected only by membranes, allowing them to overlap under the pressure of labor, changing the shape to fit the maternal pelvis (molding)

Question 16

most important fontanelles

Answer 16

the anterior (2x3cm, diamond shape) and posterior (smaller, Y- or T-shaped)

Question 17

when do the fontanelles close?

Answer 17

The posterior fontanelle closes at 6-8 weeks of life, whereas the anterior fontanelle does not close until about 18 months

Question 18

Naison

Answer 18

the root of the nose

Question 19

Glabella

Answer 19

the elevated area between the orbital ridges

Question 20

Sinciput

Answer 20

the area between the anterior fontanelle and glabella

Question 21

the name of the anterior fontanelle?

Answer 21

bregma

Question 22

name the posterior fontanelle

Answer 22

lambda

Question 23

occiput

Answer 23

the area behind the inferior to the posterior fontanelle and lambdoid sutures

Question 24

Suboccipitobregmatic diameter?

Answer 24

9.5cm. this is the presenting AP diameter when the head is well flexed (e.g. occipitotransverse or occipitoanterior position)

Question 25

Occipitofrontal diameter?

Answer 25

11cm. this is the presenting AP diameter when the head is deflexed (e.g. occipitoposterior presentation)

Question 26

Supraoccipitomental diameter?

Answer 26

13.5cm. this is the presenting AP diameter in a brow presentation and the longest diameter of the head (from vertex to chin)

Question 27

what diameter is the presenting AP diameter in face presentation?

Answer 27

Submentobregmatic 9.5cm
It extends from the lower jaw to the center of the anterior fontanelle

Question 28

The average circumference of the term fetal head is?

Answer 28

34.5 cm
measured in the occipitofrontal plane