Vacuum Cup Placement: The Flexion Point Location
The vacuum cup should be placed over the flexion point (also called the reflection point), which is located approximately 3 cm anterior to the posterior fontanelle along the sagittal suture, corresponding to the area overlying the sagittal suture where optimal flexion of the fetal head occurs.
Anatomical Location of the Flexion Point
The flexion point represents the pivot point around which the fetal head flexes during descent through the birth canal. Proper identification and cup placement at this location is critical for successful assisted vaginal delivery.
Misplacement of the vacuum cup away from the flexion point can result in inadequate flexion or unintended hyperextension of the fetal head, which increases the risk of failed vacuum delivery and potential fetal injury 1.
The flexion point is anatomically distinct from other fetal skull landmarks and must be identified precisely to achieve optimal traction mechanics during vacuum-assisted delivery 1.
Clinical Implications of Proper Cup Placement
Correct cup placement at the flexion point maximizes the mechanical advantage during traction, allowing the fetal head to maintain or achieve proper flexion as it descends through the pelvis.
When the cup is placed correctly at the flexion point, traction forces are transmitted through the optimal axis, promoting flexion rather than deflexion of the fetal head 1.
Deflexion of the fetal head, which can occur with improper cup placement, is an independent risk factor for cesarean delivery (adjusted odds ratio 5.83,95% CI 2.47-13.73), emphasizing the importance of correct technique 2.
Critical Safety Considerations
Vacuum extraction should never be used during cesarean delivery, as it can cause significant fetal injury including intracranial and subgaleal hemorrhage 3, 1.
The use of vacuum at cesarean delivery is explicitly not recommended by current guidelines due to the high risk of serious neonatal complications 1.
Prerequisites for any assisted vaginal birth include that the fetal head must be engaged and its lowermost part at or below the level of the ischial spines 4.
Common Pitfalls to Avoid
Avoid placing the cup too posteriorly (over the posterior fontanelle itself), as this will not achieve the flexion point and may result in scalp trauma without effective traction 1.
Do not attempt vacuum delivery when the fetal head position is uncertain—ultrasound confirmation of fetal head position (occiput anterior, transverse, or posterior) should be performed when clinical examination is unclear 2.
Never use vacuum extraction in the setting of cord prolapse, as this requires full cervical dilation and is inappropriate for emergency management 5.