true conjugate(redirected from obstetric conjugate diameter)
the diameter that represents the shortest diameter through which the head must pass in descending into the superior strait and measures, by means of x-ray, the distance from the promontory of the sacrum to a point on the inner surface of the symphysis a few millimeters below its upper margin.
a radiographic measurement of the distance from the upper margin of the symphysis pubis to the sacral promontory. It is usually 1.5 to 2 cm less than the diagonal conjugate. See also conjugate.
In obstetrics, the distance between the midline superior point of the sacrum and the upper margin of the symphysis pubis. It is the anteroposterior diameter of the pelvic inlet, estimated by subtracting 1.5 to 2 cm from the measurement of the diagonal conjugate.Synonym: conjugata vera
See also: conjugate