obstetric conjugate

true conjugate

[TA] 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. Synonym(s): conjugata vera [TA], obstetric conjugate diameter, obstetric conjugate

ob·stet·ric con·ju·gate

(ob-stet'rik kon'jŭ-găt) The shortest diameter through which the fetal head must pass in descending into the superior strait; as measured by 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.