Measurements of the fetal skull

Measurements of the fetal skull-

1. Diameter of the fetal skull

These are the diameter the birth canal must stretch to allow the head to pass during labour. The lagest being mento vertical 13.5cm.

1.           Sub-Occipito Bregmatic (9.5cm)

2.           Sub-Occipito Frontal (10cm)

3.           Occipito Frontal (11.5m)

4.           Mento Vertical (13.5cm)

5.           Sub Mento Vertical(11.5)

6.           Sub-mento Bregmatic (9.5cm)

7.           Biparieta (9.5cm)

8.           Bitemporal (8.2cm).

2. Circumferences

·              Sub-ocicpito bregmatic: is measurement taken round the occipital protuberance, parietal eminences and the bregma. It is the circumference which passes through the pelvis in a well flexed head 33cm.

·              Occipito Frontal: It is measured through posterior fontanel, parietal eminence and the orbital ridge. It is found in an erect head-military attitude 33-36 cm.

·              Sub-occipito frontal: It is taken round the perimeter of sub-occipito frontal 35cm.

·              Mento vertical: It is measured round the chin up to the vertex. It is found in partly extended head –(Brow) . It is the largest diameter of the fetal skull 38 cm.

3. Attitude of the head

This determines diameter that pass through the pelvis.

1.           Vertex Presentation: A well flexed head. It is the mostfavourable. engaging diameters are sub-occipito bregmatic of 9.5cm, biparieta 9.5 cm and the circumference entering the brim is sub-occipito bregmatic 33cm.

2.           Military attitude – deflexed head. The head is more erect.Engaging diameters are occipito frontal 11.5cm Biparietal 9.5cm bitemporal 8.2cm. and circumference occipito frontal 35cm.

3.           Face Presentation: Extended head. The head is completelyextended. The engaging diameter is sub-mento bregmatic 9.5cm, Bitemporal 8.2cm. sub-mento vertical of 11.5cm will descent the vaginal orifice.

4.           Brow presentation: Partially extended head mostunfavourable presentation. Normal delivery is rarely possible if it does not change the attitude. The engaging diameter is mento vertical 13.5cm, Bitemporal 8.2cm and circumference is mento vertical 38cm.