56. Anatomy of the bony female pelvis and the fetal skull Flashcards
common pelvic shapes
- Gynecoid (50%)
- Android (30%)
- Anthropoid (25%)
4.Platypelloid (rare<3%)
describe a Gynecoid pelvis
round inlet, sidewalls are straight, ischial spines are not prominent (diameter >10cm)
good prognosis for vaginal delivery
describe a Android pelvis
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
describe Anthropoid shape of the pelvis
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
describe Platypelloid shape of pelvis
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
what 4 bones make up the bony pelvis?
the sacrum (5 fused vertebrae), coccyx, and 2 innominates (composed of the ilium, ischium, and pubis)
The anterior superior edge of the 1st sacral vertebra is called ?
promontory, which protrudes slightly into the cavity of the pelvis
The pelvis is divided into
the false pelvis above and the true pelvis below the linea terminalis
The only obstetric function of the false pelvis?
is to support the pregnant uterus
how is The true pelvis formed?
by the sacrum and coccyx posteriorly and by the ischium and pubis laterally and anteriorly
what 4 imaginary planes is the pelvis divided into?
•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
The fetal skull consists of ?
a base and a vault (the cranium)
structure of the base
large, ossified, firmly united, and noncompressible bones serving to protect the vital structures within the brain stem and its spinal connections
the cranium consists of?
the occipital bone posteriorly, 2 parietal bones laterally, and 2 frontal and temporal bones anteriorly
what are the structure of the cranial bones at birth?
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)
most important fontanelles
the anterior (2x3cm, diamond shape) and posterior (smaller, Y- or T-shaped)
when do the fontanelles close?
The posterior fontanelle closes at 6-8 weeks of life, whereas the anterior fontanelle does not close until about 18 months
Naison
the root of the nose
Glabella
the elevated area between the orbital ridges
Sinciput
the area between the anterior fontanelle and glabella
the name of the anterior fontanelle?
bregma
name the posterior fontanelle
lambda
occiput
the area behind the inferior to the posterior fontanelle and lambdoid sutures
Suboccipitobregmatic diameter?
9.5cm. this is the presenting AP diameter when the head is well flexed (e.g. occipitotransverse or occipitoanterior position)
Occipitofrontal diameter?
11cm. this is the presenting AP diameter when the head is deflexed (e.g. occipitoposterior presentation)
Supraoccipitomental diameter?
13.5cm. this is the presenting AP diameter in a brow presentation and the longest diameter of the head (from vertex to chin)
what diameter is the presenting AP diameter in face presentation?
Submentobregmatic 9.5cm
It extends from the lower jaw to the center of the anterior fontanelle
The average circumference of the term fetal head is?
34.5 cm
measured in the occipitofrontal plane
