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Usually the fetal head engages in the occipito-anterior position (more often left occipito-anterior (LOA) rather than right) and then undergoes a short rotation to be directly occipito-anterior in the mid-cavity. Malpositions are abnormal positions of the vertex of the fetal head relative to the maternal pelvis. Malpresentations are all presentations of the fetus other than vertex.
Predisposing factors to malpresentation include:
- Multiple pregnancy.
- Abnormalities of the uterus, eg fibroids.
- Partial septate uterus.
- Abnormal fetus.
- Placenta praevia.
See separate article Breech Presentations for more detailed discussion.
- Breech presentation is the most common malpresentation, with the majority discovered before labour. Breech presentation is much more common in premature labour.
- Approximately one third are diagnosed during labour when the fetus can be directly palpated through the cervix.
- After 37 weeks, external cephalic version can be attempted whereby an attempt is made to turn the baby manually by manipulating the pregnant mother's abdomen.
- If the pelvis is normal and estimated fetal weight is 2,500-4,000 g, assisted breech delivery with experienced staff is believed to be as safe as Caesarean section; approximately 50% of women aiming for vaginal delivery will achieve this.
- Women who have an elective Caesarean section for a breech presentation in their first pregnancy have approximately a 1 in 10 chance of having an elective Caesarean section for a breech presentation in their second pregnancy.
- When the fetus is positioned with the head on one side of the pelvis and the buttocks in the other (transverse lie), vaginal delivery is impossible.
- This requires Caesarean section unless it converts or is converted late in pregnancy. The surgeon may be able to rotate the fetus through the wall of the uterus once the abdominal wall has been opened. Otherwise, a transverse uterine incision is needed to gain access to a fetal pole.
- Internal podalic version is no longer attempted.
- This is the most common malposition where the head initially engages normally but then the occiput rotates posteriorly rather than anteriorly. Approximately 10% of labours begin this way, but many correct in labour.
- The occipito-posterior position results from a poorly flexed vertex. The anterior fontanelle (four radiating sutures) is felt anteriorly. The posterior fontanelle (three radiating sutures) may also be palpable posteriorly.
- It may occur because of a flat sacrum, poorly flexed head or weak uterine contractions which may not push the head down into the pelvis with sufficient strength to produce correct rotation.
- Occasionally, epidural analgesia relaxes the pelvic floor such that the occiput sinks into it instead of being pushed to the correct position.
- As occipito-posterior position pregnancies often result in a long labour, close maternal and fetal monitoring are required. An epidural is often recommended and it is essential that adequate fluids be given to the mother.
- The mother may get the urge to push before full dilatation but this must be discouraged. If the head comes into a face to pubis position then vaginal delivery is possible as long as there is a reasonable pelvic size. Otherwise, forceps or Caesarean section may be required.
- The head initially engages correctly but fails to rotate and remains in a transverse position.
- Alternatives for delivery include:
- If the second stage is reached, the head must be manually rotated with Kielland's forceps or delivered using vacuum extraction. This is inappropriate if there is any fetal acidosis because of the risk of cerebral haemorrhage.
- Therefore, there must be immediate provision for a failure of forceps delivery to be changed immediately to a Caesarean. The trial of forceps is therefore often performed in theatre.
- Some centres prefer to manage by Caesarean section without trial of forceps.
- Face presents for delivery if there is complete extension of the fetal head.
- Face presentation occurs in 1 in 300 deliveries.
- With adequate pelvic size, and rotation of the head to the mento-anterior position, vaginal delivery should be achieved after a long labour.
- Backwards rotation of the head to a mento-posterior position requires a Caesarean section.
- The fetal head stays between full extension and full flexion so that the biggest diameter (the mento-vertex) presents.
- Brow presentation occurs in 1 in 500 deliveries.
- Brow presentation is usually only diagnosed once labour is well established.
- The anterior fontanelle and super orbital ridges are palpable on vaginal examination.
- Unless the head flexes, a vaginal delivery is not possible, and a Caesarean section is required.
Further reading & references
- Managing Complications in Pregnancy and Childbirth - Labour with an overdistended uterus, World Health Organization
- de Leeuw JP, de Haan J, Derom R, et al; Mortality and early neonatal morbidity in vaginal and abdominal deliveries in breech presentation. J Obstet Gynaecol. 2002 Mar;22(2):127-39.
- Coughlan C, Kearney R, Turner MJ; What are the implications for the next delivery in primigravidae who have an elective caesarean section for breech presentation? BJOG. 2002 Jun;109(6):624-6.
- Chamberlain G, Steer P; ABC of labour care: unusual presentations and positions and multiple pregnancy. BMJ. 1999 May 1;318(7192):1192-4.
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
|Original Author: Dr Colin Tidy||Current Version: Dr Gurvinder Rull|
|Last Checked: 26/10/2010||Document ID: 568 Version: 22||© EMIS|