Fetal Skull & Maternal Pelvis Relationship.pdf

Gyn/best notes

1. Fetal Skull & Maternal Pelvis
Relationship
WASIKE ANTONY
MBChB
4.2

2. Introduction
Fetalskullistosomeextendcompressibleandmademainlyof
flatbonesformingavault,thisisanchoredtotherigidand
incompressiblebonesatthebaseoftheskull
Theflatbonesofthevaultareunitedtogetherbynon-ossified
membranesattachedtothemarginsofthebones,thesearecalled
thesuturesandfontanels

3. FETAL SKULL ANATOMY

5. REGIONS OF THE FETAL SKULL
1. Vertex:
It is a quadrangular area bounded
❖ anteriorly by the bregma and coronal sutures
❖posteriorly by the lambda and lambdoid sutures and
❖laterally by lines passing through the parietal eminences.
2. Brow:
It is an area bounded on
❑one side by the anterior fontanel and coronal sutures and
❑on the other side by the root of the nose and supraorbital ridges of either side.

6. REGIONS OF SKULL CONT’D
3. Face:
It is an area bounded
❑One side by root of the nose and supraorbital ridges and
❑On other side by the junction of the floor of the mouth and
the neck.
Sinciput is the area lying in front of the anterior fontanel
and corresponds to the area of brow and,
the occiput is limited to the occipital bone.

8. SUTURES
Of the many sutures and
fontanels, the following are
of obstetric significance.
✓Sagittal suture.
✓Coronal sutures.
✓Frontal suture.
✓Lambdoid sutures.

9. Importance of sutures
1.It permits gliding movement of one bone over the other during moulding of the head
while head passes through pelvis during labor.
2.Sagittal suture identification gives an idea of head engagement and degree of internal
rotation when digital palpation is done.
3.Helps to assess the degree of moulding of the head.

10. FONTANELS
1.Anterior fontanel: it's diamond shaped, It’s floor ossifies by 18 months
after birth
Importance:
Its palpation through internal examination denotes the degree of flexion of the
head.
It facilitates moulding of the head.
It helps in accommodating the marked brain growth
 Palpation of the floor reflects intracranial status-depressed in dehydration,
elevated in raised intracranial tension.

11. 2.Posterior fontanel:
It is triangular in shape and measures about 1.2 × 1.2
cm
Its palpation through internal examination denotes the
degree of flexion of the head.
It denotes the position of the head in relation to maternal
pelvis

12. Diameters of fetal skull
The engaging diameters of the fetal skull depends on the degree of fetal head
flexion.
The transverse diameters associated with the mechanism of labor include;
❑Biparietal diameter ~9.5 cm
✓ Extends between the two parietal eminences
❑Super sub-parietal diameter ~8.5 cm
✓Extends from the point placed below one parietal eminence to a point placed above the
other parietal eminence
❑Bitemporal diameter ~ 8.0 cm
✓Distance between antero-inferior ends of the coronal sutures
❑Bimastoid diameter ~ 7.5cm
✓Distance between tips of the mastoid process, its diameter is incompressible

13. DIAMETERS OF SKULL

16. Different fetal head presentations/cephalic
presentations
1. Normal (fully flexed) & occiput anterior position
✓Its ideal and most common presentation for birth(about 95% of
births)
✓The fetal head is in the vertex presentation with the smallest
possible diameter (suboccipitobregmatic diameter ~9.5 cm).
✓Fetal head engages and descents smoothly through the birth
canal.
✓Cervical dilation and descent follow the expected pattern.
✓Fetal head rotates naturally and mother can deliver with minimal
assistance resulting into lower rates of perineal tears.

17. 2. Deflexed & malpositioned presentations
A) Occiput posterior(OP) position.
❑Most common malposition, its often called ‘’face to pubes ‘’ for the baby
CONSQUENCES OF OP POSITION
❖The fetal head presents a larger diameter to the pelvis resulting into prolonged and
arrested descent
❖Intense persistent back pain (back labor)
❖Early rupture of membranes
INTERVETION
❑ many OP babies will rotate spontaneously to OA during descent especially in roomy pelvis
❑OP delivery is possible but associated with higher risk of perineal tears some requiring
manual rotation or C-section if there’s arrest of descent

18. 3. Extended head presentations
B. BROW PRESENTATION
❑The fetal head is partially extended and the brow (forehead )is the presenting part
and this presents the largest possible diameter(mento-vertebral diameter ~13.5 cm)
to the pelvis.
CONSEQUENCES OF BROW PRESENTATION
❖Vaginal delivery is impossible and results in obstructed labour due to the arrest
of descent as the fetal head engages the maternal pelvis.
❖High risk of uterine rupture.
INTERVENTION
❑In persistent brow presentation, C-section is required.

19. C.) FACE PRESENTATION
➢Fetal head fully extended and the face is the presenting part
➢The critical factor is the position of the fetal chin (mentum)
CONSEQUENCES OF FACE PRESENTATION
oProlonged labour due to slow descent
INTERVENTION
o depends on the chin position;
✓If mentum Anterior;
The vaginal delivery is often possible, the neck can flex under the pubic bone, allowing
the neck to act as the pivot.
✓If mentum Posterior;
The vaginal delivery is impossible, the is locked , C-section is required.

22. MATERNAL PELVIS
An articulated pelvis is made
up of four bones;
❖Two hip bones (innominate
bones) , Each hip bone is
formed by fusion of 3
smaller bones the ilium,
ischium and pubis
❖Sacrum
❖Coccyx
The four bones are connected
by four main joints
❑Two sacro-iliac joints
❑Sacro-coccygeal
❑Symphysis pubis

24. False pelvis
It’s formed by the iliac portions of the
innominate bones and is limited above
by the iliac crests
OBSTETRIC FUNCTION
support the enlarged uterus during
pregnancy as well as the abdominal organs
BOUNDARIES
Posteriorly; lumbar vertebrae
Laterally; iliac fossa
Anteriorly ; lower anterior abdominal wall
True pelvis
Forms the canal through which the fetus pass
BOUNDARIES
Posteriorly; sacrum and coccyx
Laterally; ischium and parts of the ilium
Anteriorly; pubic bones and symphysis pubis
ITS FURTHER DIVIDED INTO
✓Inlet
✓Mid-pelvis
✓outlet

25. The bony landmarks on the brim of the pelvis from
anterior to posterior on each side are;
1.Upper border of symphysis pubis
2.Pubic crest
3.Pubic tubercle
4.Pectineal line
5.Iliopubic eminence
6.Iliopectineal line
7.Sacroiliac articulation
8.Anterior border of the ala of sacrum
9.Sacral promontory

26. PELVIC PLANE BOUNDARIES KEY DIAMETERS
Pelvic inlet
Anterior; Pubic symphysis
Laterally; iliopectineal line
Posterior'; sacral promontory
ANTERO-POSTERIOR
✓Anatomical(True) conjugate~11.0cm
✓Obstetric conjugate~10 cm
✓Diagonal conjugate~12 cm
TRANSVERSE DIAMETER
~13.0cm
Midpelvis(pelvic
cavity)
Not precisely bounded by a single plane❑AP diameter ~ 12.0 cm
❑Interspinous diameter~ 10.9cm
Pelvic
outlet(inferior
aperture)
Anterior; pubic arch
Laterally; ischial tuberosities
Posterior; coccyx
➢AP diameter~ 9.5-12.5 cm
➢Intertuberous diameter~11.0 cm

28. Diameters of pelvis

29. Measurement of diagonal conjugate
The patient is placed in dorsal position
Two fingers are introduced into the vagina.
The fingers are to follow the anterior sacral
curvature
In normal pelvis, it is difficult to feel the sacral
promontory or at best can be felt with difficulty
The fingers are then mobilized under the
symphysis pubis and a marking is placed over
the gloved index finger by the index finger of the
left hand

30. CLASSIFICATION OF THE PELVIS( Caldwell
and Moloy)

31. CLASSIFICATION OF THE PELVIS
CONT.

32. CLASSIFICATION OF THE PELVIS
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33. CLASSIFICATION OF THE PELVIS
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34. CLASSIFICATION OF THE PELVIS
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35. References
Human Labor & Birth 6
th
Edition
Dutta’s textbook of Obstetrics 8
th
Edition
Obstetrics by ten teachers 20th edition by Louise C.