The pelvic inlet usually is considered to be contracted if its shoest anteroposterior diameter is less than 10 cm or if the greatest transverse diameter is less than 12 cm. The anteroposterior diameter of the inlet is commonly approximated by manually measuring the diagonal conjugate, which is approximately 1.5 cm greater. Therefore, inlet contraction usually is defined as a diagonal conjugate of less than 11.5 cm. Ref: Cunningham F.G., Leveno K.J., Bloom S.L., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 20. Abnormal Labor. In F.G. Cunningham, K.J. Leveno, S.L. Bloom, J.C. Hauth, D.J. Rouse, C.Y. Spong (Eds), Williams Obstetrics, 23e.