Conjugate diameter

Conjugate Diameter

The conjugate diameteris an important anatomical measurement in obstetrics, particularly in the assessment of the female pelvis. It is one of the key dimensions used to evaluate the size and shape of the pelvic inlet, which is crucial for determining the feasibility of vaginal delivery.

Anatomy and Definition

The conjugate diameter, also known as the true conjugateor obstetric conjugate, is the anteroposterior diameter of the pelvic inlet. It is measured from the sacral promontory to the upper margin of the pubic symphysis. This measurement is critical because it represents the shortest anteroposterior distance through which the fetal head must pass during childbirth.

Measurement

Direct measurement of the true conjugate is not possible clinically due to its location. Instead, the diagonal conjugateis measured during a pelvic exam. The diagonal conjugate extends from the lower border of the pubic symphysis to the sacral promontory. The true conjugate is then estimated by subtracting approximately 1.5 to 2 cm from the diagonal conjugate.

Clinical Significance

The size of the conjugate diameter is a determinant of pelvic adequacy for vaginal delivery. A conjugate diameter of less than 10 cm may indicate a contracted pelvis, which could complicate vaginal delivery and necessitate a cesarean section. Obstetricians assess this measurement along with other pelvic dimensions to predict potential delivery complications.

Related Pelvic Diameters

In addition to the conjugate diameter, other pelvic diameters are assessed:

• Transverse diameter: The widest horizontal distance across the pelvic inlet.
• Oblique diameter: The distance from one sacroiliac joint to the opposite iliopubic eminence.
• Diagonal conjugate: Used to estimate the true conjugate.

Also see

• Pelvic inlet
• Pelvimetry
• Obstetrics
• Cesarean section