Flexion point in relation to fetal skull landmarks

The flexion point is the location on the fetal head where outward traction pulls the head so as to allow flexion at the neck while keeping the mentovertical diameter in the direction of the birth canal. In the normally molded fetal head, the flexion point is in the midline, over the sagittal suture, approximately 6 cm from the anterior fontanelle and 3 cm from the posterior fontanelle. Since most of the commonly used vacuum cups have a diameter between 50 and 70 mm, when the center of the cup is placed over the flexion point, the edges of the cup should be approximately 3 cm from the anterior fontanelle and just at the edge of the posterior fontanelle. The anterior fontanelle is the reference point for checking the application because access to the posterior fontanelle is partially blocked once the extractor cup is in place.