Useful defi nitions when discussing the presenting part • Presentation is the lowermost part of the fetus presenting to the pelvis. In more than 95% of cases the vertex is the presenting part and is called normal presentation. Any other presentation (e.g. face, brow, breech, and shoulder) is called malpresentation. • Denominator is the most defi nable peripheral landmark of the presenting part, i.e. occiput for the vertex, mentum for the face, and sacrum for the breech presentation. • Position of the presenting part is the relationship of the denominator to the fi xed points of the maternal pelvis, i.e. sacrum posteriorly, pubic symphysis anteriorly, sacro-iliac joints posterolaterally, and ileo-pectineal eminences anterolaterally. • Station is the relationship of the most prominent leading part of the presenting part to the ischial spines expressed as ± 1,2,3cm. 2 In the vertex presentation more than 90% present in the occipito- anterior position, i.e. the occiput is in the anterior half of the pelvis and is called the normal position. If the occiput is pointing laterally or is in the posterior half of the pelvis, it is called malposition and is associated with defl exed head presenting a larger anteroposterior diameter of the vertex (11.5cm) and, hence, diffi culties with progress of labour
Posted on: Tue, 12 Aug 2014 23:08:24 +0000
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