ANTERO-POSTERIOR DIAMETER OF FETAL SKULL AND TRANSVERSE DIAMETER OF FETAL SKULL

The fetal skull having two types of diameter.

1-Anterior posterior diameter.

2- Transverse diameter

ANTERIOR POSTERIOR DIAMETER OF THE FETAL SKULL.

There are six anterior posterior diameter present in the fetal skull.

1-Suboccipitobregmatic(9.5cm)

2-Suboccipitofrontal(10cm)

3-occipitofrontal(11.5cm)

4-Mentovertical(13.5cm)

5-Submentovertical (11.5cm)

6-Submentobregmatic(9.5cm)

1-SUBOCCIPITO BREGMATIC

It is the diameter starting from below the occipital protuberance to the midst of the anterior fontanelle or bregma.(9.5cm)

When the fetal head is occipital anterior position and the fetal head attitude is flexion then the engaging diameter of the fetal head is suboccipito-bregmatic(9.5cm).it is normal to deliver the baby.seen in vertex presentation.

2-SUBOCCIPITOFRONTAL

This is the diameter of the fetal skull starting from below the occipital protuberance to centre of the frontal suture.it is 10 cm.

This diameter seen in occipital anterior position of the fetal head when the fetal attitude is slight deflexed and it is 10cm.and it is allso normal.seen in vertex presentation.

3-OCCIPITOFRONTAL

This is the diameter 11.5cm , starting from the occipital protuberance to the glabella

This diameter seen in occipito posterior position of the fetal head with deflexion head.it is difficult for the baby to get through the pelvis in occipito-frontal diameter.so there may be obstructive delivery.

4-MENTOVERTICAL

This is the diameter starting from the point of the chin to the highest point on the vertex.

This diameter seen in brow presentation of the fetal head(14cm)). Due to larger diameter it is difficult for the delivery of baby. So there may be LSCS according to doctors decision.

5-SUBMENTOVERTICAL

It is 11.5cm and starting from the point where the chin meets the neck to the highest point on the vertex.

This diameter seen in face presentation with partially extended head.

6-SUBMENTOBRAGMATC

Starting from the point where the chin joint with the neck to bregma.it is 9.5 cm and this diameter seen in face presentation.which is malposition. The attitude of head is complete extension so that it is difficult to deliver the baby.

TRANSVERSE DIAMETER OF THE FETAL SKULL.

There are four transverse diameter of the fetal skull.

1- Biparietal diameter

2-Super-subparietal diameter

3- Bitemporal diameter

4-Bimastoid diameter

BIPARIETAL DIAMETER

It is extend between two parietal eminence.measure 9.5cm and largest transverse diameter of the fetal skull

SUPER-SUBPARIETAL DIAMETER

Two parietal eminence situated on the parietal bone .and super-subparietal diameter starting from one point below the parietal eminence to the point above the other parietal eminence.it is 8.5cm

BITEMPORAL DIMETER

It is the distance between the antero-inferior ends of the coronal suture.it is 8cm.

BIMASTOID DIAMETER

It is the distance between the tips of two mastoid process. It is 7.5cm. and it is the smallest diameter of the fetal skull.