Presenting diameters

Presenting diameters of foetal head and how does it affect the labour process. Also the outcomes and few management options are included too.

1. Presenting Diameters of Fetal
Head and it's Importance

2. Anatomy of Fetal Skull

3. 
Fetal cranium made of 5 bones- 2 parietal bones / 2
frontal bones and the occipital bone

These are held together by membranous structures
called sutures- permit movements of bones during
labour

There are 4 prominent sutures
1. Coronal suture : separates frontal bones from
parietal bones
2. Sagittal suture : separates two parietal bones
3. Lamboid suture : separates occipital bone from
parietal bones
4. Frontal suture : separates two frontal bones.

4. 
Fontanelle : When two or more sutures meet, there is
an irregular membranous part between them called
fontanelle

There are two important fontanelles
1. Anterior fontanelle ( bregma ) : Diamond shaped
area at the junction of coronal and sagittal sutures.
AP/transverse diameter 3 cm. Fused around ~18
months
2. Posterior fontanelle ( lambda ) : Small triangular
area at the junction of sagittal and lamboid sutures
(closes 2-3 months after birth )

6. Regions of Fetal Head

Occiput : The bony prominence that lies behind
posterior fontanelle

Vertex : Diamond shaped area between anterior and
posterior fontanelle

Sinciput : Area in front of anterior fontanelle. Includes
forehead.

Brow – between bregma and root of nose

lying below root of nose and supra orbital bridges

8. Diameters of Fetal Head

Five important diameters.
1. Suboccipito-bregmatic
diameter
2. Suboccipitofrontal
diameter
3. Occipitofrontal diameter
4. Mentovertical diameter
5. submentobregmatic
diameter

9. Suboccipito-bregmatic
diameter

The diameter is from suboccipital
region to centre of the bregma.

Diameter = 9.5 cm

Fetal head circumference is
smallest (32 cm )

Head well flexed

Flexed vertex presentation

10. Suboccipito-frontal
diameter

Diameter calculated from
prominence at mid frontal
bone to the under-surface of
the occipital bone where it
joins neck

The diameter is 10.5 cm

Vertex is partially deflexed.

Results in occipito-posterior
position.

11. Occipito-frontal diameter

Diameter extends from the
prominent point of mid-frontal
bone to the most prominent point
of occipital bone

The diameter = 11.5 cm

Fetal head circumference ~ 34.5
cm

Vertex is deflexed

Associated with Direct occipito-
posterior position.

12. Occipito-posterior position
It is a vertex presentation in which
the occiput is placed posteriorly .
It can be:-
1.Right occipto-posterior (the
commonest)
2.Left occipto-posterior.
3.Direct occipto-posterior
Associated diameters are
1. Suboccipito frontal diameter
2. Occipitofrontal diameter

13. Incidence :Incidence :
In 20% of cases the occiput is posterior at the beginning of
labour .
Causes :-Causes :-
1. Pelvic Factors:- 50% of cases are associated with anthropoid
pelvis or android pelvis .
2.Fetal Factors:- Marked deflection of the fetal head due to high
pelvic inclination or anterior wall placenta .
3.Uterine Factor:- Abnormal uterine contraction which may be
the cause or effect .

14. DiagnosisDiagnosis
Abdominal Examination
Features suggesting the diagnosis include
-backache during labour.
-flattening of the abdomen below the umbilicus .
-the fetal limbs are more easily felt near the midline on both
sides.
-The head not engaged and feels larger than usual

15. Problems associated with Occiput Posterior –
-the head faces the front of the mother's pelvis instead of
turning toward the mother's back.
-delivered with the head facing the ceiling,which is often a
more difficult way to deliver.
vaginal examination
-Elongated bag of membrane which is likely to rupture early .
-High deflexed head with the anterior fontanelle in the centre of
the pelvis .

16. - A large episiotomy may be required.
- OP may lead to dysfunctional labour (in primigravida).
- Contraction may be painful and accompanied by backache
Mechanism of Labour in OP position
First and second stage of labour usually prolonged .
-membrane usually rupture early with the hazards of cord
prolapse and infection .
-In favorable circumstances (90% of cases) good uterine
contraction result in good flexion of the head and the occipt
rotates 3/8 of the circle (135c
0
) anteriorly and deliver as
occipito-anterior position .

17. In unfavorable circumstances (10% of cases) the occiput
1. Fail to rotate and remain in the oblique diameter of the pelvis .
2. Rotate anteriorly 1/8
th
of circle (short rotation) and the head
become arrested in the transverse diameter of the pelvis (deep
transverse arrest) .
3. Rotate posterioly 1/8
th
of the circle to lie on the sacral hollow
this called direct-occipto- posterior position .
And if the fetus is small & pelvis is Adequate spontenous delivery
can occur as face to pubic.

18. ManagementManagement
- Unless there is fetal hypoxia or other complication labour is
allowed to proceed with the following special instructions .
-Provide adequate analgesia (an epidural is ideal).
-Prevent dehydration with intravenous fluid.
-You may need to promote uterine contraction with oxytocin .
-Good monitoring for progress of labour ,fetal condition and
maternal condition .

19. -In the majority of cases anterior rotation of the occipt is
completed and the baby is delivered as occipto-anterior.
-In direct occipto-posterior delivery as face to pubis may
occur ,The perineum should be protected by a generous
episiotomy.
Persistent –occipto posterior and deep transverse arrest .
-If the fetal head is not engaged caesarian section is the
treatment of choice .
-If the fetal head is engaged the treatment will be one of
the following .

20. 1) Manual rotation and delivery by forceps as
occipto-anterior .
2) Rotation to occipto-anterior and extraction using
kielland’s forceps .
3) Ventouse (vacuum extraction).
4) Caesarean section if the above lines of treatment
fail or there is other complicating factor .
5) Craniotomy when the fetus is dead .

21. Mento-vertical diameter

Diameter extending from the
chin to furthest point of vertex.

Measures 13cm

Largest antero-posterior
diameter

Head is partially extended.

Associated with brow
presentation

22. Brow presentation

Incidence:
ranges from 1:1000 to 1:3500

Rarest malpresentation

The presenting diameter 13.5cm
(mento-vertical )

Incompatible with vaginal delivery
Causes

Prematurity

Multiple pregnancies

Goiter or hygroma

23. DiagnosisDiagnosis

Abdominal examination-
suspect if both chin and occiput are palpable
head doesn't descend below ischeal spines

Vaginal examination
Palpate supra orbital ridges/nose, anterior
fontanelle.
Cant palpate chin.

24. ManagementManagement

Watch and wait : may become face or vertex
presentation

If progress is slow or the brow persists
caesarian section

25. Submento-bregmatic
diameter

The diameter extending from
just behind chin to the centre
of bregma

Measures 9.5cm

Head is fully extended

Associated with face
presentation

26. Face presentation
Incidence :
1:600- 1:1500

Due to hyper-extension of fetal head

Presenting diameter 9.5 cm
(submento-bregmatic diameter )

Engagement of fetal head late

Progression of labour slow

Probably due to lack of molding of
facial bones

27. CausesCauses

Fetal anomalies.
The most common anomaly that causes face presentation
is anencephaly. Anencephalic babies present face first
because of the faulty development of the cranium.
Tumors on the neck or back may also cause extension of
the head.

Pelvic contractures or android pelvis. This is the major
factor. It accounts for about 40% of face presentations.

Fetopelvic disproportion

Multiparity

28. 
Preterm birth

Polyhydramnios. When the membranes rupture the
rush of fluid may cause the head to extend as it
descends.

Coils of umbilical cord around the neck.
DiagnosisDiagnosis

Vaginal examination
The orbital ridges/nose/malar eminences/ mentum/
mouth and gums

29. Management
In the chin-anteriorchin-anterior
position prolonged labor
is common. Descent
and delivery of the head
by flexion may occur.
In the chin-posterior chin-posterior
position, however, the fully
extended head is blocked
by the sacrum. This
prevents descent and
labour is arrested.

30. Management
Chin-Anterior PositionChin-Anterior Position
If the cervix is fully dilated:
Allow to proceed with
normal childbirth;
If there is slow progress
and no sign of obstruction,
augment labor with
oxytocin;
If descent is unsatisfactory,
deliver by forceps.
If the cervix is not fully
dilated and there are no
signs of obstruction:
augment labor with
oxytocin.
Chin-Posterior PositionChin-Posterior Position
If the cervix is fully dilated:
Deliver by caesarean
section.
If the cervix is not fully
dilated
Monitor descent, rotation
and progress. If there are
signs of obstruction,
deliver by caesarean
section.
*Do not perform vacuum Do not perform vacuum
extraction for face extraction for face
presentation.presentation.

31. Thank You!!