The ischial spines are designated as an important landmark in labour are delivery because the distance between the spines is:
A. The narrowest diameter of the pelvis
B. The widest measurement of the pelvis
C. A measurement of the floor of the pelvis
D. A measurement of inlet of the birth canal
Correct Answer: A. The narrowest diameter of the pelvis
Explanation
The ischial spines are an important landmark in labour and delivery because the distance between them represents the narrowest diameter of the pelvis.
Explanation
- The distance between the two ischial spines is called the interspinous (bispinous) diameter.
- It measures approximately 10–10.5 cm.
- This diameter is the narrowest fixed bony diameter of the birth canal (mid-pelvis).
- During labour, the fetal head station is assessed in relation to the ischial spines:
- 0 station = head is at the level of the ischial spines.
- Prominent ischial spines may indicate difficulty in vaginal delivery.
Correct concept
👉 Distance between the ischial spines = narrowest diameter of the pelvis (interspinous diameter)
Other Options Details
Here is a clear explanation of all the options, related to pelvic measurements in obstetrics:
A. The narrowest diameter of the pelvis
- This usually refers to the bispinous diameter (interspinous diameter).
- It is the shortest and narrowest diameter of the pelvic canal, measured between the two ischial spines.
- Clinically very important because it represents the mid-pelvis, where obstruction to labor commonly occurs.
- Normal value: ~10–10.5 cm
B. The widest measurement of the pelvis
- This refers to the transverse diameter of the pelvic inlet.
- It is the largest diameter of the pelvic inlet, extending across the widest part.
- Important for engagement of the fetal head.
- Normal value: ~13–13.5 cm
C. A measurement of the floor of the pelvis
- This refers to the intertuberous diameter (bi-ischial diameter).
- It measures the distance between the ischial tuberosities.
- It is a diameter of the pelvic outlet, representing the pelvic floor.
- Normal value: ~11 cm
- Important during the expulsion stage of labor.
D. A measurement of the inlet of the birth canal
- This refers to the anteroposterior diameter of the pelvic inlet (true conjugate / obstetric conjugate).
- It measures the distance from the sacral promontory to the pubic symphysis.
- Critical for determining whether the fetal head can enter the pelvis.
- Obstetric conjugate: ~10.5 cm
Summary Table
Option Pelvic Area Key Diameter A Mid-pelvis Narrowest (bispinous) B Pelvic inlet Widest (transverse) C Pelvic outlet Floor (intertuberous) D Pelvic inlet AP diameter (conjugate)
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Writer: Vandita Singh, Lucknow (GS India Nursing Group