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from Section 6 - Late Prenatal – Obstetric Problems
Introduction
The concepts of breech presentation, unstable lie, malpresentations, and malposition have not changed for many years but the diagnostic tools and management options change periodically as new management techniques are developed and the evidence for their use improves. Early in pregnancy the position, presentation, and lie of a fetus are irrelevant, and they only become important near term and at delivery.
Definitions
Lie. The relationship of the longitudinal axis of the fetus to the longitudinal axis of the mother's uterus. The terms commonly used are:
• Longitudinal lie: the fetal longitudinal axis is parallel to the uterine longitudinal axis.
• Oblique lie: The fetal axis is diagonal to the uterine axis.
• Transverse lie: The fetal longitudinal axis is perpendicular to the uterine axis.
• Unstable lie: The fetal lie continues to change at or near term (usually from 37 weeks onwards). The lie varies between longitudinal, oblique, and transverse.
Presentation. The fetal body part that is adjacent to the birth canal in the lower uterine segment closest to the cervix. The presentations seen in practice are cephalic (head), face, brow, shoulder, arm, hand, breech, or compound (combination of head or limbs with a limb or cord)
Position. The relationship of the presenting part to the maternal pelvis.
• In a cephalic presentation the occiput (vertex) is used to describe the fetal position.
• In a breech presentation the sacrum is used to describe the position.
• In a brow position the bregma is used to describe the position.
• In a face presentation the mentum is used to describe the position.
With a cephalic presentation, any position other than an occipitoanterior (OA) position is considered a malposition. Examples of malpositions in a cephalic presentation include occipitoposterior (OP) and occipitotransverse (OT). Asynclitism, a sideways tilt of the head, is also a malposition.
Other Important Definitions
Breech presentation. The fetus is in a longitudinal lie with buttocks adjacent to the birth canal.
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