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Female pelvic shape: Distinct types or nebulous cloud?

02 July 2015
13 min read
Volume 23 · Issue 7

Abstract

The objective of this study was to re-evaluate the Caldwell-Moloy (1933) classification of female pelvic shape, which has been traditionally, and still is currently, taught to students of midwifery and medicine. Using modern pelvimetric methodologies and geometric morphometric (GM) analysis techniques, we aim to elucidate whether these classic female pelvic types are an accurate reflection of the real morphometric variation present in the female human pelvis.

GM analysis was carried out on sets of pelvic landmarks from scans of women living in a contemporary Western Australian population. Sixty-four anonymous female multi-detector computer tomography (MDCT) scans were used for most of the study and 51 male scans were also examined for comparison.

Principle component analysis (PCA) found that there was no obvious clustering into the four distinct types of pelvis (gynaecoid, anthropoid, android and platypelloid) in the Caldwell-Moloy classification, but rather an amorphous, cloudy continuum of shape variation.

Until more data is collected to confirm or deny the statistical significance of this shape variation, it is recommended that teachers and authors of midwifery, obstetrics and gynaecological texts be more cautious about continuing to promote the Caldwell-Moloy classification, as our results show no support for the long taught ‘four types’ of pelvis.

For well over 50 years, students of midwifery, obstetrics, gynaecology and related professions have been taught the Caldwell-Moloy classification of the female pelvis. While recognising variation and mixed types, the current e-book of Mayes’ Midwifery (MacDonald and Magill-Cuerden, 2011), is typical in its frank reporting and use of that system. ‘Although there are four recognised pelvic categories (Caldwell et al, 1940: Table 24.1), variations within these categories can occur. Some women may have mixed features, such as a gynaecoid posterior pelvis and android fore-pelvis’ (Burden and Simons, 2011: 286). The 10th edition of Clinical Obstetrics also gives Caldwell-Maloy classification system similar prominence (Gopalan and Jain, 2005).

The basic ‘four types of pelvis’ categorisation persists to this day and is evidenced by the fact that it is taught in many universities and colleges globally and regularly cited in university-level midwifery course compulsory texts, such as Mayes Midwifery (MacDonald and Magill-Cuerden, 2011) and Myles’ Textbook for Midwives (Fraser and Cooper, 2009) and referred to in recent studies on female pelvic shape variation (e.g. Hashemi et al, 2010). The four types of pelvis categorisation persists even though the initial simple classification was subsequently extended by Caldwell et al (1940) to include 14 sub-types, and that it has also been criticised, for example, for being overtly racist (Geller and Stockett, 2007).

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