Before applying a vacuum cup for operative vaginal delivery, correct placement is verified. Where is the flexion point located?
- A On the sagittal suture, 3 cm anterior to the posterior fontanelle ✓
- B Directly over the posterior fontanelle
- C Over the anterior fontanelle, centered on the sagittal suture
- D Midway between the posterior fontanelle and the occipital protuberance
Correct answer: A. On the sagittal suture, 3 cm anterior to the posterior fontanelle
Explanation
The flexion point lies on the sagittal suture approximately 3 cm in front of the posterior fontanelle. Cup application here keeps the head fully flexed so the suboccipitobregmatic diameter, the shortest presenting diameter, engages. Placement directly over the posterior fontanelle or too far forward produces deflexion, increasing the presenting diameter and causing failure of descent and greater scalp trauma. This is why malpositioned cups lead to pop-offs and failed deliveries.
Reference: RCOG Green-top Guideline No. 26: Operative Vaginal Delivery, 2011 ed.
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Written and medically reviewed by the StethoPrep medical team.