During vacuum-assisted vaginal delivery, correct placement of the cup at the 'flexion point' determines success. Where is this point located?

• A Directly over the posterior fontanelle
• B Midway between the two parietal eminences
• C 3 cm posterior to the anterior fontanelle
• D On the sagittal suture, 3 cm anterior to the posterior fontanelle ✓

Explanation

The flexion point lies on the sagittal suture 3 cm in front of the posterior fontanelle, approximately 6 cm behind the anterior fontanelle. Cup placement here keeps traction perpendicular to the occiput, preserves flexion, and draws along the occipitobregmatic diameter, the smallest presenting diameter of the vertex. Placement directly over the posterior fontanelle or nearer the anterior fontanelle promotes deflexion, increasing detachment rates, failed delivery, and scalp trauma.

Reference: Munro Kerr's Operative Obstetrics, 13th ed.

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Written and medically reviewed by the StethoPrep medical team.