During vacuum-assisted vaginal delivery, correct placement of the cup over the flexion point maximizes flexion of the fetal head and minimizes cup detachments. Where is the flexion point located?

• A On the sagittal suture, 3 cm in front of the posterior fontanelle ✓
• B Directly over the posterior fontanelle
• C Directly over the anterior fontanelle
• D Midway between the anterior fontanelle and the posterior fontanelle

Explanation

The flexion point lies on the sagittal suture approximately 3 cm anterior to the posterior fontanelle, which places the centre of the cup near the mentovertical diameter and keeps the head fully flexed during traction. Cup placement over either fontanelle or midway between them produces deflexion or asynclitism, increasing the traction force needed, causing more pop-offs, and raising the risk of scalp trauma and cephalhematoma.

Reference: Williams Obstetrics, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.