Diameters of The fetal skull having two types of diameter.

Understanding the Diameters of the Fetal Skull from Obstetrics and GynaecologiCal Nursing for ANM, GNM ,BSC and MSC Nursing 

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 of the fetal skull starting from below the occipital protuberance to the center of the anterior fontanelle or bregma.(9.5cm)

(Occipital protuberance means it is a bony prominence on occipital bone .

Bregma means – Coronal suture sagital suture meet in this junction.

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.It is most favorable position for child birth.

 

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- SUBMENTOBRAGMATIC

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 1FETAL 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.

 

MCQ from this topic 

1-The Suboccipitobreagmatic diameter of the fetal  determined from:

a- From below the occipital protuberance to centre of the Bregma.

b-From the occipital protuberance to glabella 

c- From below the occipital protuberance to the center of the frontal suture

d- It is from the point where chin joints the neck 

 

Explanation – Subocciptobregmatic diameter starts from below the occipital protuberance to centre of the Bregma ( here occipital protuberance means a bony prominence on the fetal skull and Bregma means where coronal suture and sagittal ,suture meet at this junction.

2- In which position the Suboccipitobreagmatic engagement diameter- obtained: 

a– Right occipito anterior position 

b- Left occipito anterior position 

c- Right occipito posterior position 

d- Right occipito anterior position and left occipito anterior position 

• Explanation – In LOA ( left occipito anterior position and Right occipito anterior position you can get this diameter which is favorable for normal delivery.

ANS- d

3- During time of delivery if the mother is not facing any fetal distress or any  abnormal condition and fetal head is ROA position or in LOA position then which mode of delivery is most Expected:
a) Spontaneous vaginal delivery
b) Lower Segment Cesarean Section (LSCS)
c) Forceps delivery
d) Delivery by vacuum

 Answer: a) Spontaneous vaginal delivery 

 

4-In Diameters of  fetal skull Occipitofrontal diameter determined from:

a- From below the occipital protuberance to centre of the Bregma.

b-From the occipital protuberance to glabella 

c- From below the occipital protuberance to the center of the frontal suture

d- It is from the point where chin joints the neck 

ANS- b- It is from the occipital protubarance to glabella  

5- In which position of the fetus The occipito frontal engagement diameter obtained.

a– Right occipito anterior position 

b- Left occipito anterior position 

c- Right occipito posterior position and left occipito posterior position 

d- Right occipito anterior position and left occipito anterior position 

EXPLANATION -Occipitofrontal -11.5cm is the Engagement diameter in occipito posterior position of the fetal skull 

ANC- C- Right occipito posterior position and left occipito posterior position 

6-Submentobregmatic diameter- of the fetal skull extends from: 

• a-It is from the point where chin joints the neck to the center of the Bregma
• b- Left occipito anterior position 
• c- Right occipito posterior position and left occipito posterior position 
• d- Right occipito anterior position and left occipito anterior position 
• EXPLANATION – Submentum means  (the point beneath the chin)
   Bregma means (the anterior fontanelle on the top of the skull)
  It measures 9.5 cm
  It is the engaging diameter in face presentation (when the fetal head is fully extended) – In 6 r 6-which Presentation of the fetal skull Submentobregmatic -9.5cm engaging diameter obtained.
• a- Face presentation
•  b- brow presentation 
• c- Vertex presentation 

        d- Breech presentation

•  EXPLANATION –When the fetal head is fully extended then Face will become presenting part .and Submentobregmatic diameter -9.5 become Engaging diameter of the fetal skull.
• ANS- FACE presentation  
• 7 – Submentovertical diameter diameter extends from: 
• a-It is from below the occipital protubarance to center of the anterior fontanelle or Bregma 
• b- It is from below the occipital protubarance to the center of the frontal suture .
• c-It is from occipital protubarance to the glabella 
• d-It is from the point where the chin joints the neck to the highest point on the vertex.
• ANS-d- it is from the point where the chin joints the neck to the highest point on the vertex 
• 8 The Submentovertical diameter of the fetal skull measures 
• a- 9.5cm 
• b- 10 cm 
• c–13.5cm
• -d-11.5cm 
• ANS-d-11.5cm 

9-Mentovertical diameter of the fetal skull is determined from 

• a-It is from the point where the chin joins the neck to the center of the Bregma.
• b/-It is from the point where the chin joins the neck to the highest point on the vertex 
• It is from the point of the chin to the highest point on the vertex 
• d-It is from the occipital protubarance to the glabella.
• ANS-It is from the point of the chin of the chin to the highest point on the vertex 

10-Right measurement of Biparietal diameter is ;

• A-9.5cm 
• B-9 CM 
• C-8.5 CM 
• D-7.5 CM
• ANS-9.5CM

 

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