Abnormal Pelves

As with all other human characteristics, there are variations in the size and shape of the female pelvis. Caldwell et al (1940) cited in (Sweet 1997) showed this from pelvic radiographs. They described the four main types as: gynaecoid, anthropoid, android and platypelloid. These variations are usually of genetic origin with herediatary or racial characteristics. (See activity 3.). The progress and outcome of labour will differ in a woman who labours with any of these types of pelvis. (See activity 5.)

Other abnormalities may be acquired from disease or from injury. Usually the fetus is of a size to fit the pelvis, therefore difficulties in labour should not arise. Where a deformity is apparent which alters the shape or causes pelvic contraction then problems in labour can occur. This is referred to as cephalo-pelvic disproportion (CPD). This may be a generally contracted pelvis or an asymmetrical pelvis. Pelvic contraction will alter the outcome of labour but other factors apart from the size and shape of the pelvis will determine this. The size of the fetus, the strength of uterine contractions, degree of moulding, postion and flexion of the head will all be determining factors. Pelvic contraction can be divided into three groups.

Slight pelvic contraction; where the true conjugate is over 9.5cms a vaginal delivery is likely.

Moderate pelic contraction; the true conjugate is between 8.5cms and 9.5cms. There is a possibility of vaginal delivery .

Gross pelvic contraction; the true conjugate is less than 8.5cms. Vaginal delivery is unlikely.