Measurement from lower boarder of symphysis pubis to the center of the promontory of the sacrum to know the pelvis capacity is known as
A. Diagonal conjugate
B. Obstetrical conjugate
C. Transverse diameter of the brim
D. Transverse diameter of the pelvic outlet
Correct Answer: A. Diagonal conjugate
Explanation
The measurement described is called the Diagonal Conjugate.
Explanation
- The diagonal conjugate is the distance measured from the lower border of the symphysis pubis to the center of the sacral promontory.
- It is the only anteroposterior diameter of the pelvic inlet that can be measured clinically during a vaginal examination.
- This measurement is used to assess pelvic capacity indirectly in obstetrics.
Importance
- The diagonal conjugate helps in estimating the obstetrical conjugate, which is the shortest anteroposterior diameter of the pelvic inlet and the most important diameter for vaginal delivery.
- Since the obstetrical conjugate cannot be measured directly, it is calculated as:
Obstetrical conjugate = Diagonal conjugate − 1.5 to 2 cm
Normal values
- Diagonal conjugate: about 12.5–13 cm
- Obstetrical conjugate: about 10.5–11 cm
Clinical significance
- If the diagonal conjugate is reduced, it suggests a contracted pelvis, which may lead to difficulty in labor or obstructed delivery.
✅ Correct answer: Diagonal conjugate
Other Options Details
Here is a clear obstetrics-focused description of each option, with definitions, measurements, and clinical importance:
A. Diagonal Conjugate
- Definition: Distance from the lower border of the pubic symphysis to the sacral promontory.
- Measurement: About 12.5–13 cm.
- Clinical importance:
- It is the only anteroposterior diameter of the pelvic inlet that can be measured clinically during vaginal examination.
- Used to estimate the obstetrical conjugate.
- Formula:
Obstetrical conjugate = Diagonal conjugate − 1.5 to 2 cm
B. Obstetrical Conjugate
- Definition: Distance from the sacral promontory to the nearest point on the posterior surface of the pubic symphysis.
- Measurement: About 10.5–11 cm.
- Clinical importance:
- It is the shortest and most important anteroposterior diameter of the pelvic inlet.
- Determines whether the fetal head can enter the pelvis.
- Cannot be measured directly; calculated from the diagonal conjugate.
C. Transverse Diameter of the Brim (Pelvic Inlet)
- Definition: Maximum distance between the two farthest points on the linea terminalis.
- Measurement: About 13–13.5 cm.
- Clinical importance:
- It is the widest diameter of the pelvic inlet.
- Important for engagement of the fetal head, especially in gynecoid pelvis.
D. Transverse Diameter of the Pelvic Outlet (Intertuberous Diameter)
- Definition: Distance between the inner borders of the ischial tuberosities.
- Measurement: About 10.5–11 cm.
- Clinical importance:
- It is the widest transverse diameter of the pelvic outlet.
- Can be increased slightly during labor due to mobility of the coccyx.
- Important for passage of the fetal shoulders and head during delivery.
Summary Table
Diameter Location Average Size Clinical Importance Diagonal conjugate Pelvic inlet 12.5–13 cm Clinically measurable Obstetrical conjugate Pelvic inlet 10.5–11 cm Most important for engagement Transverse diameter of brim Pelvic inlet 13–13.5 cm Widest inlet diameter Transverse diameter of outlet Pelvic outlet 10.5–11 cm Widest outlet diameter
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Writer: Vandita Singh, Lucknow (GS India Nursing Group