Obstetrics Simplified - Diaa
It is a cephalic presentation in which the head is completely extended.
About 1:300 labours.
- Primary face:
- It is less common.
- It occurs during pregnancy.
- It is usually due to foetal causes which may be:
- Anencephaly: due to absence of the bony vault of the skull
and the scalp while the facial portion is normal.
- Loops of the cord around the neck.
- Tumours of the foetal neck e.g. congenital goitre.
- Hypertonicity of the extensor muscles of the neck.
- Dolicocephaly: long antero-posterior diameter of the head,
so as the breadth is less than 4/5 of the length.
- Dead or premature foetus.
- Secondary face:
- It is more common.
- It occurs during labour.
- It may be due to:
- Contracted pelvis particularly flat pelvis which allows
descent of the bitemporal but not the biparietal diameter leads
to extension of the head.
- Pendulous abdomen or marked lateral obliquity of the uterus.
- Further deflexion of brow or occipito - posterior positions.
- Other causes of malpresentations as polyhydramnios and placenta
- Right mento-posterior (RMP).
- Left mento-posterior (LMP).
- Left mento-anterior (LMA).
- Right mento-anterior (RMA), are the more common positions.
- Right mento-transverse (lateral), left mento-transverse, direct
mento-posterior and direct mento-anterior are rare and usually transient
The first position (RMP) corresponds to the first normal position (LOA)
as the back should be to the left and anterior in the first position.
Mento-anterior are more common than mento-posterior as most cases arise
from more deflexion of the head in occipito-posterior position usually in
flat contracted pelvis.
During pregnancy (difficult)
- The back is difficult to feel.
- The limbs are felt more prominent in mento-anterior position.
- The chin may be felt on the same side of the limbs as a horseshoe-shaped
rim in mento-anterior position.
- In mento-posterior, a groove may be felt between the occiput and
the back particularly after rupture of the membranes.
- Second pelvic grip: the occiput is at a higher level than the sinciput.
- The FHS are heard below the umbilicus through the foetal chest wall
in mento-anterior position.
- Ultrasound or X-ray: confirms the diagnosis and may identify associated
foetal anomalies as anencephaly.
shows the following identifying features for face:
- supra-orbital ridges,
- the malar processes,
- the nose (rubbery and saddle shaped),
- the mouth with hard areolar ridges.
- the chin.
Late in labour, the face becomes oedematous (tumefaction) so it can be
misdiagnosed as a buttock (breech presentation) where the two cheeks are
mistaken with buttocks and the mouth with anus and the malar processes with
the ischial tuberosities. The following points can differentiate in-between:
mouth and malar processes form the apexes of a triangle.
is on the same line with the ischial tuberosities.
|The gum is
felt hard through the mouth.
||No hard object
through the anus.
finger may be sucked by the foetal mouth during vaginal examination.
does not suck the finger.
Mechanism of Labour
- Engagement by submento-bregmatic diameter 9.5 cm.
- Increased extension.
- Internal rotation of chin 1/8 circle anteriorly.
- Flexion: is the movement by which the head is delivered in mento-anterior
position when the submental region hinges below the symphysis. The vulva
is much distended by the submento-vertical diameter 11.5 cm.
- External rotation.
Engagement is delayed because:
- The biparietal diameter does not pass the plane of pelvic inlet
until the chin is below the level of the ischial spines and the face
begins to distend the perineum.
- Moulding does not occur as in vertex presentation.
- Long anterior rotation 3/8 circle (2/3 of cases):
- so the head is delivered as mento-anterior.
- In about 1/3 of cases one of the following may occur:
- Deep transverse arrest of the face: when the chin rotates 1/8
- Persistent mento-posterior: when no rotation occurs.
- Direct mento-posterior: When the chin rotates 1/8 circle
In the last 3 conditions no further progress occurs and labour is obstructed.
Direct mento-posterior, unlike direct occipito-posterior, cannot be delivered
- Delivery should occur by extension while the head is already maximally
- As the length of the sacrum is 10 cm and that of neck is only 5
cm, the shoulders enter the pelvis and become impacted while the head
still in the pelvis, thus the labour is obstructed.
Management of Labour
Exclude: - Foetal anomalies and - Contracted pelvis.
- First stage: as in occipito-posterior.
- Second stage:
- Spontaneous delivery usually occurs.
- Forceps delivery may be indicated in prolonged 2nd stage.
- Episiotomy is necessary because of over distension of the vulva.
- First stage: as mento-anterior.
- Second stage:
- Wait for long anterior rotation of the mentum 3/8 circle and
the head will be delivered as mento-anterior. During this period
oxytocin is used to compete inertia which is common in such conditions
as long as there is no contraindication. Failure of this long rotation
is more common than in occipito-posterior position so earlier interference
is usually indicated.
- Failure of long anterior rotation 3/8 circle or development
of foetal or maternal distress at any time, is managed by:
- Caesarean section: which is the safest and the current alternative
in modern obstetrics.
- Manual rotation and forceps extraction as mento-anterior, or
- Rotation and extraction by Kielland forceps.
- In the last 2 methods the head should be engaged but they
are hazardous to both the mother and foetus so they are nearly
out of modern obstetrics.
- Craniotomy: if the foetus is dead.
The face of the foetus is oedematous after delivery so the mother is
assured that this will be spontaneously relieved within few days.
See complications of malpresentations and malposition.
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Edited by Aldo Campana,