Question:medium
The presenting diameter of a fully flexed fetal head is:
The presenting diameter of a fully flexed fetal head is:
Show Hint
Full flexion presents the smallest, roughly 9.5 cm diameter.
Updated On: Jun 23, 2026
- Suboccipito-bregmatic diameter
- Suboccipito-frontal diameter
- Occipito-frontal diameter
- Occipito-posterior position
Show Solution
The Correct Option is A
Solution and Explanation
Step 1: Flexion of the fetal head determines which anteroposterior diameter engages the pelvis; maximal flexion brings the narrowest diameter forward.
Step 2: With complete flexion the suboccipito-bregmatic diameter, about $9.5$ cm, presents, running from the suboccipital region to the bregma, and it corresponds to the smallest head circumference.
Step 3: Increasing deflexion progressively substitutes the larger suboccipito-frontal and occipito-frontal diameters, while occipito-posterior names a position, not a diameter. The diameter of the fully flexed head is therefore suboccipito-bregmatic.
\[\boxed{\text{Suboccipito-bregmatic diameter}}\]
Step 2: With complete flexion the suboccipito-bregmatic diameter, about $9.5$ cm, presents, running from the suboccipital region to the bregma, and it corresponds to the smallest head circumference.
Step 3: Increasing deflexion progressively substitutes the larger suboccipito-frontal and occipito-frontal diameters, while occipito-posterior names a position, not a diameter. The diameter of the fully flexed head is therefore suboccipito-bregmatic.
\[\boxed{\text{Suboccipito-bregmatic diameter}}\]
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