Question

Which of the following diameters of fetal skull does not measure 9.5 cm?

• A. \( \text{Occipito frontal} \)
• B. \( \text{Sub occipito bregmatic} \)
• C. \( \text{Sub mento bregmatic} \)
• D. \( \text{Biparietal diameter} \)

Hint:

\textbf{Obstetrics: Fetal Skull Diameters.} Familiarity with the key diameters of the fetal skull and their average measurements is essential for understanding the mechanisms of labor and potential difficulties during childbirth. The biparietal and suboccipito-bregmatic diameters are particularly important for assessing fetal head engagement and passage through the pelvis.

Answer 1

The Correct Option is A

We need to consider the average measurements of the different diameters of the fetal skull at term: \begin{itemize} \item Occipito frontal diameter: This extends from the occipital protuberance to the glabella (the smooth part of the forehead between the eyebrows) and measures approximately 11.5 cm. \item Sub occipito bregmatic diameter: This extends from the suboccipital region (below the occipital protuberance) to the center of the anterior fontanelle (bregma) and measures approximately 9.5 cm. This is the presenting diameter in a well-flexed vertex presentation. \item Sub mento bregmatic diameter: This extends from the point of the chin (mentum) to the center of the anterior fontanelle (bregma) and measures approximately 9.5 cm. This is the presenting diameter in a face presentation. \item Biparietal diameter: This is the transverse diameter between the two parietal eminences and measures approximately 9.5 cm. This is a crucial diameter for engagement of the fetal head in the pelvis. \end{itemize} Therefore, the occipito frontal diameter does not measure 9.5 cm; it is larger, approximately 11.5 cm.