During a vacuum-assisted delivery, which fetal scalp application point is biomechanically most appropriate for traction to reduce the risk of cup detachment and fetal injury?

• A Anterior fontanelle
• B Posterior fontanelle directly
• C Occipital protuberance
• D Flexion point — 3 cm anterior to posterior fontanelle on the sagittal suture ✓

Explanation

The 'flexion point' for vacuum cup application is 3 cm (or 1–2 cm anterior to the posterior fontanelle) on the midline sagittal suture. Correct placement at this point ensures traction in the axis of the birth canal while promoting flexion of the fetal head, thereby reducing the suboccipito-bregmatic diameter presented. Application at the anterior fontanelle promotes deflexion (increasing the diameter), increasing the risk of cup detachment and scalp injury. The posterior fontanelle itself is not the cup centre point; it should be the reference for measuring the 3 cm anterior placement.

Reference: Williams Obstetrics, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.