Anatomical Variations in the Female Pelvis: The Caldwell-Moloy Classification

Since 1933, when Caldwell and Moloy (1) first came out with their classification of the female pelvis, several articles have been written by the same authors and their co-workers on the general use of x-ray in the study of the mechanics of obstetrics, particularly as it relates to pelvic form and fetal-pelvic relationships. Other writers have added to the literature follow-up reports to evaluate further the application of these studies by careful clinical-roentgenologic correlation. It has been rather definitely shown that measurements are not the entire story and that the x-ray can be of aid in determining the course of labor over and above the procedures which deal primarily with the mensuration of the fetal head and maternal pelvis. The problem is not entirely one of size, but includes pelvic form and fetal-pelvic relationships. If one disregards the clinical correlation, particularly with border-line disproportions, one will easily mislead the clinician and discredit an otherwise valuable roentgen procedure, however important fetal cephalometry and maternal pelvimetry may seem to be in a specific case. A recent article by Nicholson and Allen (2) we believe deserves some comment. These authors criticize the Caldwell-Moloy classification of the female pelvis because of its lack of precision. They feel that there are so many subclassifications under the four parent types that the method of classification becomes unwieldy. To quote these authors: “Classification may be a fine weapon in the armament of science, but classification without precise definition is simply the negation of science and can only lead to the multiplication of types. until every example has a type of its own.” They seek to disprove (1) the fact that the android pelvis is a male pelvis and that it is associated with other male stigmata in the female, (2) that the android pelvis and to some extent the anthropoid pelvis are associated with narrow outlets, and (3) that the android pelvis is associated with difficult labor, propositions which they say Caldwell and Moloy have propounded. They attempt to produce proof that the android pelvis is associated with neither contraction of the pubic angle nor with difficult labor. They also point out that any deformities in the pelvis which lead to difficult labor are due to deficient nutrition in childhood. Some of these ideas cannot go unchallenged. In the first place, Caldwell and Moloy never “argued” that the android pelvis was necessarily associated with difficult labor. They did say that a relatively small android pelvis is more apt to cause trouble than a relatively small gynecoid pelvis because of the difficult mechanism that may be associated with the android type. In those pelves which are borderline or normal as to size, the pelvic form may play a major role. In this regard Nicholson and Allen have missed a very important point.