In face presentation, the denominator is the:
A. Vertex
B. Frontal eminence
C. Acromion
D. Mentum
Correct Answer: D. Mentum
Explanation
In face presentation, the denominator is the mentum (chin).
Explanation
- Denominator: It is the fixed bony point on the presenting part used to describe the position of the fetus in the maternal pelvis.
- In face presentation, the fetal head is fully extended.
- Because of this complete extension, the chin (mentum) becomes the most prominent and fixed bony landmark.
- Therefore, fetal positions are named as:
- Mento-anterior
- Mento-posterior
- Mento-transverse
Clinical importance
- Vaginal delivery is possible only in mento-anterior position, as further extension allows the head to deliver.
- Mento-posterior position usually leads to obstructed labour, because further extension is not possible.
✅ Correct answer: Mentum (chin)
Other Options Details
These terms refer to presenting parts of the fetus in different types of presentations during labour.
Explanation of each option 👇
A. Vertex
- Meaning: The area of the fetal head between the anterior and posterior fontanelles.
- Associated presentation: Vertex presentation (most common and normal).
- Clinical importance:
- Head is well flexed
- Engaging diameter: suboccipito-bregmatic (9.5 cm)
- Most favorable for normal vaginal delivery
B. Frontal eminence
- Meaning: The prominent part of the fetal forehead.
- Associated presentation: Brow presentation (partial extension of the head).
- Clinical importance:
- Head is midway between flexion and extension
- Engaging diameter: mento-vertical (≈13.5–14 cm)
- Vaginal delivery is usually difficult or impossible unless it converts to face or vertex
C. Acromion
- Meaning: The bony tip of the fetal shoulder.
- Associated presentation: Shoulder presentation (transverse lie).
- Clinical importance:
- Long axis of fetus is transverse
- Presenting part is shoulder
- Vaginal delivery is not possible
- Requires cesarean section
D. Mentum
- Meaning: The fetal chin.
- Associated presentation: Face presentation (complete extension of the head).
- Clinical importance:
- If mentum is anterior, vaginal delivery may be possible
- If mentum is posterior, vaginal delivery is not possible
- Engaging diameter: submento-bregmatic (9.5 cm)
Summary Table
Presenting part Presentation Delivery outcome Vertex Vertex Normal vaginal delivery Frontal eminence Brow Difficult / usually not possible Acromion Shoulder Cesarean section Mentum Face Possible only if mentum anterior
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Writer: Vandita Singh, Lucknow (GS India Nursing Group