Introduction
Normally the fetus lies longitudinally with a well-flexed vertex presenting. Any other lie or presentation is a malpresentation, and an abnormal position of the vertex (e.g. occipito-posterior) is a malposition.
Transverse and oblique lie
The fetal long axis lies across the uterus; the shoulder or arm may present. It occurs in about 1 in 300 term births.
- Causes: multiparity (lax uterus), placenta praevia, polyhydramnios, uterine anomalies or fibroids, contracted pelvis, preterm birth, second twin.
- Diagnosis: wide uterus, no pole in the fundus or pelvis, head in one flank; confirm with ultrasound.
- Management: before labour, look for a cause; external cephalic version at 37 weeks if no contraindication; admit from 37 weeks if the lie is unstable. A persistent transverse lie in labour → caesarean section. Neglected transverse lie leads to shoulder presentation, arm prolapse and uterine rupture.
- A second twin in transverse lie can be turned by internal podalic version and breech extraction.
Atypical cephalic presentations
Risk factors for deflexed presentations
Multiparity, contracted pelvis, large or small fetus, polyhydramnios, fetal anomalies (anencephaly, goitre), cord around the neck.
Diagnosis in labour
- Vaginal examination: sutures and fontanelles. The small (posterior) fontanelle (Y-shaped) leads in a flexed vertex; the anterior fontanelle (diamond) and orbit ridges suggest a brow; the mouth, nose and malar bones suggest a face (do not confuse with breech).
- Ultrasound confirms the position.
Face mento-anterior can deliver, face mento-posterior and a persistent brow cannot: those need caesarean section.