The smallest anteroposterior diameter of the pelvic inlet is called the

The obstetric conjugate is the shoest distance between the promontory of the sacrum and the symphysis pubis. It generally measures 10.5 cm. Because the obstetric conjugate cannot be clinically measured, it is estimated by subtracting 1.5 to 2 cm from the diagonal conjugate, which is the distance from the lower margin of the symphysis to the sacral promontory.