Diameters of Skull
Diameters of Skull-
The engaging diameter of the fetal skull depends on the degree of flexion present.-
| Diameters | Measurement | Attitude of the Head | Presentation |
|
Suboccipitobregmatic - Extends from the nape of the neck to the center of the bregma |
9.5 cm | Complete flexion |
Vertex |
|
Suboccipito-frontal - Extends from the nape of the neck to the anterior end of the anterior fontanel or center of the sinciput |
10 cm | Incomplete flexion |
Vertex |
|
Occupitofrontal - Extends from the occipital eminence to the root of the nose (Glabella) |
11.5 cm | Marked deflexion |
Vertex |
|
Mento-vertical - Extends from the midpoint of the chin to the highest point on the sagittal suture |
14 cm | Partial extension |
Brow |
|
Submentovertical - Extends from junction of floor of the mouth and neck to the highest point on the sagittal suture |
11.5 cm | Incomplete extension | Face |
|
Submentobregmatic - Extends from junction of floor of the mouth and neck to the center of the bregma |
9.5 cm | Complete extension |
Face |
The transverse diameters which are concerned in the mechanism of labor are
Biparietal diameter (9.5 cm )
It extends between two parietal eminences. Whatever may be the position of the head, this diameter nearly always engages.
Super-subparietal (8.5 cm)
It extends from a point placed below one parietal eminence to a point placed above the other parietal eminence of the opposite side.
Bitemporal diameter (8 cm)
It is the distance between the anteroinferior ends of the coronal suture.
Bimastoid diameter ( 7.5 cm)
It is the distance between the tips of the mastoid processes. The diameter is incompressible and it is impossible to reduce the length of the bimastoid diameter by obstetrical operation.