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|
Extends from the nape of the neck to the center of the bregma
|9.5 cm||Complete flexion
Extends from the nape of the neck to the anterior end of the anterior fontanel or center of the sinciput
|10 cm||Incomplete flexion
Extends from the occipital eminence to the root of the nose (Glabella)
|11.5 cm||Marked deflexion
Extends from the midpoint of the chin to the highest point on the sagittal suture
|14 cm||Partial extension
Extends from junction of floor of the mouth and neck to the highest point on the sagittal suture
|11.5 cm||Incomplete extension||Face|
Extends from junction of floor of the mouth and neck to the center of the bregma
|9.5 cm||Complete extension
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.