Haider Al hulialiHaider Al Ali

Normal Pelvis, types of female pelvis and fetal skull

Bony pelvis : it is made up of four bones : the sacrum ,

coccyx , and two innominates (composed of the ilium , ischium ,and pubis).

Pelvic anatomy

Joints

Pelvis is divided into the false pelvis and the true pelvis •The false pelvis is bordered by the lumbar vertebrae posteriorly , an iliac fossa bilaterally ,and the abdominal wall anteriorly .•It supports the pregnant uterus .

•The true pelvis is a bony canal and is formed by the sacrum and the coccyx posteriorly and by the ischium and pubis laterally and anteriorly .•The posterior wall is twice the length of the anterior wall.•The true pelvis is area of concern because its dimensions are sometimes not adequate to permit passage of the fetus .

The pelvic inlet The plane of greatest diameter The plane of least diameter The pelvic outlet

Pelvic planes

Lateral Posterior Anterior Pelvic Planes

iliopectinaeal line of the innominate bones.

sacral promontory

pubic crest 1- The Pelvic Inlet

upper part of the obturator foramina

junction of S2 & S3

posterior midpoint of the pubis

2- The Plane of greatest diameter

ischial spines and sacrospinous ligaments

Lower sacrum

Lower edge of pubis

3- The Plane of least diameter (Mid-pelvic Plane)

ischial tuberosity

sacrococcygeal joint

lower pubic bone

4- The Pelvic Outlet

Pelvic Diameters

The diameters of the pelvic planes represent the amount of space available at each level .

Pelvic Inlet Pelvic inlet has five important diameters :The anteroposterior diameter : described by one of

two measurements: the true conjugate (anatomic conjugate ):

from sacral promontory to superior pubis obstetric conjugate: from sacral promontory

to posterior pubis .The transverse diameter : the widest distance

between iliopectineal linesTwo oblique diameters :from sacroiliac joint to the

opposite iliopectineal eminence The posterior sagittal diameter: from AP &

transverse intersection to the middle of sacral promontory

Plane of Greatest Diameter

The anteroposterior diameter : from the midpoint of the posterior surface of pubis to the junction of S2 and S3 vertebrae .

The transverse diameter : widest distance between the lateral borders of the plane (upper part of obturator foramina )

Plane of Least diameter (midplane )

The anteroposterior diameter :extends from the lower border of the pubis to the junction of S4 and S5 .

The transverse (bispinous ) diameter : extends between the ischial spines .

The posterior sagittal diameter : from midpoint of bispinous diameter to the junction of S4 and S5

Pelvic outlet

Anatomic anteroposterior diameter :from the inferior margin of pubis to tip of coccyx

Obstetric anteroposterior diameter : from inferior margin of pubis to sacrococcygeal joint .

Transverse diameter : between the inner surface of ischial tuberosities

Posterior sagittal diameter : from middle of transverse diameter to the sacrococcygeal joint .

Pelvic Shapes

Android

30%

Gynecoid

50%

Anthropoid

18%

Platypelloid

2%

Gynecoid

Round at the inletSide walls strightIscheal spines of average

prominenceWell-rounded sacrosciatic

notchWell-curved sacrumSpacious subpubic arch, with

an angle of approximately 90 degrees

Cylindrical shape

Android

Triangular inletConvergent Side wallsShallow sacral curveLong and narrow

sacrosciatic notchNarrow subpubic archIt is the typical male type

Anthropoid

Long narrow oval inlet (AP>transverse)

Side walls that not convergeIschial spines close, owing to

overall shapeVariable, but usually posterior,

inclination of the sacrumLong sacrosciatic notchNarrow, outwardly shaped

subpubic arch

Platypelloid

Oval-shaped inlet (AP<transverse)

Straight or divergent side walls

Ischial spines close, owing to overall shape

Posterior inclination of a flat sacrum

Wide bispinous diameterA wide subpubic arch

flat shape

Clinical Pelvimetry

For assessment of obstetric capacity, most important measurements are:Obstetric conjugate of inletDistance between ischial spinesSubpubic angle & bituberous diameterPosterior sagittal of three planesCurve & length of sacrum

- It is only an estimate

- The best time is late in pregnancy when the soft tissue are distensible

Clinical Pelvimetry

palpate the SACRUMIt should be concave. Flat or convex is

abnormal

midpelvis and pelvic outlet: can’t accurately be measured clinically but it can be estimated through clinical examination.

X-ray Pelvimetry Its purpose is to aid in determining the need for C-S.

Other factors affecting need for C-S include: Fetal size, Force of contractions, & Position of fetus, & degree of molding

It is an accurate measure Indications:

No longer needed in cephalic presentation

Breech deliveryTo rule out pelvic abnormalities either

inherited or traumatic 2 films are needed

Lateral view – AP diameterInlet view – transverse diameter

Fetal Skull

General characteristicsSutures,Fontanelles and boneslandmarksDiametersCephalic pelvic disproportion

Objectives

Fetal Head: is the Largest and least compressible part

of the fetus

General characteristics

Base Cranium (Vault)

Large, ossified, firmly united and non-compressible

•Consists of occipital , parietal , frontal and temporal bones

•At birth thin, weakly ossified, easily compressible and interconnected only by membranes

Protects the vital structures within the brainstem

allows molding

General characteristicsfetal skull: 1-base

2-cranium

Definition:The membrane occupied spaces between

the cranial bones.

sutures

The membrane filled spaces located at the point where the sutures intersect.

fontanelle

fontanellesCharacteristics Closure

(ossification)

Anterior Fontanelle (bregma)

Diamond shape and found at

the intersection of sagittal , frontal and

coronal sutures2-3 cm (larger)

18 months of life

Posterior Fontanelle

Y or T-shaped and found at

the junction of the sagittal and

lambdoid sutures

6-8 weeks of life

Land Marks

Nasion

Glabella

1

2

35

6

7

(bregma)

(lambda)

(

sincipu

t

)

1- Nasion : root of the nose2- Glabella: elevated area between the orbital

ridges3-Sinciput(brow):the area between anterior

fontanelle and glabella4- anterior fontanelle(bregma)5- vertex the area between the fontanelles and

bonded laterally by the parietal eminence6- posterior fontanelle ( lambda)7- occiput the area behind and inferior to the

posterior fontanelle and lambdiod sutures

Land Marks

Antero-posterior diameters( 4 )

Transverse diameters ( 2 )

Diameters

Antero-posterior diameters

Length Definition Presentation

Suboccipitobregmatic

9.5cm Extends from occipital bone at the junction of the neck to AF .

When the head is well flexed as in occipitoanterior or occipitotransverse

Submentobregmatic

9.5cm from junction of neck and lower jaw to AF.

in the face presentation

Occipitofrontal

11cm from external occipital protuberance to glabella.

As in occipitoposterior presentation

Supraoccipitomental

13.5cm from vertex to chin.

In a brow presentation ( lead to CS )

Transverse diameters:

1. Biparietal(9.5cm): between the parietal

bones.

2. Bitemporal(8cm):between the

temporal bones

An obstetric condition where there is mismatch in size between (fetal head & the maternal pelvis), resulting in failure of the fetus to pass safely through the birth canal for mechanical reasons.

Cephalic pelvic disproportion

1- Absolute CPD: There is no possibility of a normal vaginal delivery (extremely rare).

Fetal (Temporary):macrosomia (diabetes) & Fetal

hydrocephalusMaternal (Permenant):

Congenitally abnormal pelvis.Damaged pelvis (RTA).Distorted pelvis (osteomalacia).

2- Relative CPD: the baby is large but would pass through the pelvis if the mechanisms of labor function correctly.

If, however, the head is deflexed or fails to rotate in the mid-cavity, then prolonged, abnormal labor will occur.

CPD:Can only truly be diagnosed after a trial of labour.May be suspected antenatally in women who are

≤ 1.58m height. Should be suspected in a women with a high head

at term, after excluding the other causes.

CPD

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