1 Anatomic Characteristics of the Fetal Head and Maternal Pelvis Du Xue , PHD Department of Obstetrics & Gynecology General Hospital of TianJin Medical University
1
Anatomic Characteristics of the Fetal Head and Maternal Pelvis
Du Xue , PHDDepartment of Obstetrics & Gynecology General Hospital of TianJinMedical University
2
Fetal head ---caranium ---sutures ---fontanelles ---landmarks ---diameters
Pelvis ---Bony pelvis ---planes ---diameters ---landmarks ---shapes
3
The fetal skull Base: to protect the vital structures ---large ---ossified ---firmly united ---noncompressible Vault(cranium): to overlap under pressure and to
change shape to confirm to the maternal pelvis (molding)
---thin ---weakly ossified ---easily compressible ---interconnected by membranes
4
Fetal Head---the cranium
Occipital bone (posteriorly) Two parietal bone (bilaterally) Two frontal bone (anteriorly) Two temporal bone (anteriorly)
5
6
Fetal Head---Sutures the membrane-
occupied space between the cranial bone
Sagittal Lambdoid Coronal Frontal
Sagittal:
Between the parietal bones;
anteroposterior direction
Divide Right and left
Lambdoid:
Extends from the posterior fontanelle laterally
Separate occipital from parietal bones
Coronal :
Extends from the anterior fontanelle laterally
Separate parietal from frontal bones
Frontal :
Between the frontal bones
Extends from the anterior fontanelle to the glabella
7
8
9
10
Fetal Head--- Fontanelles
Defininion:the membrane-filled space located at the point where the sutures intersect.
The most important of which are the anterior and posterior fontanelles.
More useful in diagnosing the fetal head position than sutures
11
intersection of sagittal, frontal, coronal sutures
diamond shaped about 2x3cm closes at 18
months after birth
The anterior fontanelle
12
The posterior fontanelle
Junction of the sagittal and lambdoid sutures
Y or T shaped closes at 6-8
weeks after birth.
13
Fetal Head--- landmarks Nasion Glabella Sinciput Anterior
fontanelle Vertex Posterior
fontanelle Occiput
14
Nasion:The root of the nose
Glabella:the elevated area between the orbital ridges
Sinciput: the area between the anterior fontanelle and the glabella
Anterior fontanelle:diamond shapedVertex:between the
fontanelles and bounded laterally by the eminences
Posterior fontanelle:Y or T shaped
Occiput:behind and inferior to the posterior fontanelle and lambdoid sutures
15
Fetal Head--- Diameters The anteroposterior diameters ---Suboccipitobregmntic diameter (9.5cm) ---Occipital frontal diameter (11cm) ---Supraoccipitomental diameter (13.5cm) ---Submentobregmatic diameter (9.5cm) Transverse diameter ---Biparietal diameter (9.5cm) ---Bitemporal diameter (8 cm) Average circumference of the term fetal head(in
the occipitofrontal plane)-----------------------(34.5cm)
16
Suboccipitobregmatic (9.5cm)
From the undersurface of occipital to the center of the ant fontanelle
Occipitalfrontal(11cm)
From external occipital protuberance to the glabella
Supraoccipitomental (13.5cm)From the vertex to the chin
Submentobregmatic (9.5cm)From the junction of the neck and lower jaw to the center of the ant fontanelle
17
Biparietal (9.5cm) largestExtend between the parietal bones
Bitempotal (8cm) shortestExtend between the temporal bones
18
19
Maternal pelvis
20
Maternal pelvis----Clinical Pelvimetry
Not all the diameters can be assesed clinically
Assess the diameters at the first prenatal visit to screen for obvious pelvic contractions or in the late pragnancy(may be less uncomfortable and more accurate)
21
Inlet plane:The obstetric conjugate The diagonal conjugate:is
approximated by measuring from the lower border of the pubis to the sacral promontary using the tip of the second finger and the point where the index finger meets the pubis.
The obstetric conjugate=the diagonal conjugate-(1.5~2cm)
normal value:11.5cm
22
Inlet plane:the sacrum The anterior surface of the
sacrum is palpated to assess its curvature.
The usual shape is concave. A flat or convex shape may indicate anteroposterior constriction throughout the pelvis.
23
Inlet plane---transverse diameter interspinal diameter
(髂前上棘间径, IS) ---23-26cm Intercristal
diameter(髂嵴间径, IC)
---26-28cm
24
25
26
Mid plane: cannot be accurately measured clinically
Bispinous diameter(10.5cm)(坐骨棘间径) ---The ischial spines are palpated carefully to
assess their prominence. the sacrospinous ligament (骶棘韧带) ---assessed by placing one finger of the ischial
spine and one finger on the sacrum in the midline ---The average length is three fingerbreadths ---A short ligament suggest a forward inclination
of the sacrum and a narrowed sacrosciatic notch
27
Outlet plane: Bituberous diameter and the infrapubic angle
Bituberous diameter(坐骨结节间径) ---first placing a fist between the ischial tuberosities ---Normal value:8.5cm or above The infrapubic angle(耻骨联合角度) ---placing a thumb next to each inferior pubic
ramus and then estimating the angle at which they meet
---<90º is associated with a contracted transverse diameter in the midplane and outlet.
28
Bituberous diameter
29
Engagement Engagement occurs when
the widest diameter of the fetal presenting part has passed through the pelvic inlet.
in cephalic presentations, the widest diameter is biparietal;intertrochanteric(breech)
When the fetal head has engaged, the bony presenting part is at the level of the ischial spine.
30
The station of the presenting part in the pelvic canal is defined as it's level above or below the plane of the ischial spine.
The level of ischial spineis assigned as “zero”, each cm above or below this level is given a minus or plus designation.
31
When the presenting is out of the pelvis, it is freely movable, it is considered to be floating.
When it has passed through the plane of the inlet ,but is not yet engaged, it is considered to be dipping.
32
33
34
35
36