Malpresentation & cord prolapse

Malpresentation & cord prolapse
Introduction and definitions
The lowest pole of the fetus that presents to the lower uterine segment and the cervix is called presentation. About 95% of fetuses at term present by the vertex in labour and hence is called normal presentation. The vertex is a diamond-shaped area defined by the two parietal eminences, anterior fontanel and posterior fontanel.

When the presentation is other than the vertex, that is, breech, brow, face or shoulder they are termed malpresentations.
The definitive aetiology for malpresentations is not known in the majority of cases. They may be associ¬ated with contracted pelvis, large baby, polyhydramnios, multiple pregnancy, low-lying placenta, preterm labour, anomalies of the fetus (neck tumours), uterus (congenital or acquired, e.g. lower segment fibroids).

Brow presentation
In brow presentation the head is half extended and presents to the pelvis with the largest anteroposterior diameter (mento-vertical - 13 cm).

The lower most part of the head that is palpable on vaginal examination is the forehead but it is termed as brow because the orbital ridges and the bridge of the nose are the most definable part of the presentation. The incidence is rare.
The presentation may correct itself in labour by flex¬ion and present as a vertex or undergo further extension and present as a face and may result in vaginal delivery.
Persistence of brow presentation in labour at term, is not compatible with vaginal delivery and necessitates a CS. In early labour, preparations should be undertaken for CS and time allowed to see whether flexion or extension would take place. Failure to progress in the next few hours in labour with the persistence of brow presentation is an indication for CS and not for augmentation of labour with oxytocin.
In extreme prematurity the fetus may descend as a brow and deliver as a brow or may convert to a face or vertex after it reaches the pelvic floor. Although vaginal delivery is possible in preterm fetuses there is a possibility of spinal cord damage and a CS is preferred.
Compli¬cations in labour include cord prolapse with membrane rupture and rare incidence of uterine rupture in neglected cases. In cases of intrauterine fetal death and in those with lethal malformation in the extreme preterm period, where injury to the fetus is not a concern, labour may be allowed if there is good progress in anticipation of vaginal deliv¬ery.


Face presentation:
Face presentation in which the head is fully extended occurs in approximately 1:500 to 1000 deliveries. The general causes for malpresentations apply for face presentation. There is a small chance of congeni¬tal abnormality such as anencephaly or fetal goitre and this need to be excluded by an ultrasound examination. In the majority it is due to extension of the head in a normal fetus.
The possibility of face presentation can be suspected on abdominal examination. Face presentation is confirmed on vaginal examination when the nose, eyes and the hard gum margins are palpated.
Difficulties may be encountered in recognizing the pre-sentation when the membranes are intact especially if the presenting part is high or in the presence of oedema due to few hours of labour.



The mechanism of labour has some similarity to that of the vertex. The transverse submento-bregmatic diam¬eter enters the pelvis. In the vast majority it rotates forwards to be in the mento-anterior position with the chin behind the symphysis pubis. The presenting lat¬eral (biparietal - 9.5 cm) and anteroposterior (submento-bregmatic - 9.5 cm) diameters are conducive for vaginal delivery. Descent is possible posteriorly in the pelvis when the position is mento-anterior because of large space in the lateral sacral area.
The head is born with the chin emerging under the pubic arch followed by the forehead over the perineum. If the face rotates to a mento-posterior position, although the diameters are the same as mento-anterior, the lateral dimensions of the frontal bones are large and do not per¬mit descent behind the narrow retropubic arch and hence a CS is advisable.
Even with favourable mento-lateral or anterior position if there is failure to progress the safer option for the fetus is CS in the first stage. In late second stage of labour with the face at the outlet in mento-anterior or lateral position outlet forceps delivery can be carried out by skilled personel if spontaneous delivery is not forthcoming.


Transverse Lie & Shoulder presentation:
The baby lies with its long axis transverse in the uterus, when the shoulder is usually the presenting part.
In multiparous women with singleton pregnancies shoul¬der presentation is more common without any cause due to the laxity of the uterus. However, there are known asso¬ciations and they are preterm, congenital fetal or uterine malformation, fibroids, placenta praevia and polyhydramnios. The incidence at term is about 1:400.
Transverse lie with shoulder presentation in the antenatal period cor¬rects itself to longitudinal lie with the onset of labour due to increased muscular tone of the uterus. Should rupture of membranes take place with the fetus in the transverse lie, cord prolapse, shoulder presentation and arm prolapse are likely possibilities with progressive cervical dilatation.

Diagnosis:
The abnormal shape of the uterus (the fundus being lower than expected), no fetal pole at the fundus or in the pelvic inlet, will make the diagnosis straight forward. In early labour, these findings are unchanged but an elongated bag of forewaters may be felt vaginally which could contain a limb or a loop of cord. Neglected transverse lie will, almost inevitably lead to uterine rupture.

Management:
If transverse or oblique lie discovered early in labour it can be corrected by external cephalic version if the membranes are intact. Once the lie is corrected the membranes should be ruptured & uterine contractions will maintain the longitudinal lie.
If the membranes rupture and the fetus is still in the trans¬verse lie, CS should be performed to avoid injury to the fetus or the uterus. In cases where the diagnosis is made late the fetus may be impacted in the transverse lie and safe delivery may be only possible by a CS with a midline vertical incision. Labour and sponta¬neous vaginal delivery is possible in extreme preterm and macerated fetuses.