Abnormal pelvis: Overview, Causes & Effects on Labour 

What is an abnormal pelvis?

Abnormal pelvis is a pelvis with disruption in its structure or function.  It is the main cause of prolonged or obstructed labour that necessitates cesarean delivery. 

There are different types of abnormal pelvis which are classified under two main groups.

  • Congenital abnormalities of the pelvis
  • Acquired abnormalities of the pelvis.

Congenital abnormalities of the pelvis

Justo Minor: This is like gynaecoid in shape but all the diameters of the brim cavity and outlet are proportionately reduced, it is seen in women of small status. The shoe size is less than 4.

Effects of Justo Minor pelvis  on labour

  • If the size of the baby is proportionate to the size of the pelvis,  no difficulty may be encountered, the law of compensation is observed.
  •  If the size of the baby is disproportionate to the pelvis elective cesarean section is undertaken in most cases of booked women with this type of pelvis by the obstetrician

 Naegele’s pelvis: Here the sacrum has only one wing or alae. This can occur in a woman who has limping gait for many years

Roborth pelvis: The sacrum has no wings or alae at all and so it is contracted in all directions

High Assimilation: In this type of pelvis, the last lumbar vertebra is fused to the upper part of the sacrum producing a large promontory with a subsequence reduction of anterior posterior diameter of the brim, because of this the head may fail to engage

Achondroplastic pelvis: Failure of the growth of both the long bones leading to dwarfism. This condition also affects the shape and inclination of the pelvis

Contracted pelvis: This is the type of pelvis in which the one or more essential diameter like anteroposterior position (AP), transverse, or oblique diameter of the brim, cavity and outlet of the brim is reduced by 1 cm or more.

Acquired abnormalities of the pelvis

Rachitic Pelvis: the pelvis is deformed due to ricket in early childhood. Ricket is due to lack of vitamin  D, causing non-absorption of calcium and phosphorus. The incidence of this type of pelvis is now reduced due to infant welfare facilities and health care.

Osteomalacia Pelvis: Deformity here is due to deficiency of minerals, vitamin A and D in diet. This makes the bones to be soft on the side walls of the pelvis canal, squashed together until the brim becomes a mere slit shape.

Spondylolytic  Pelvis: This is a condition where the lower lumbar vertebra slight forward to over hanged the sacral promontory thus markedly reduced the anterior posterior diameter of inlet

Fractured Pelvis: Badly healed fracture of the pelvis reduces the diameter of the brim, cavity and outlet.

Kyphotic Pelvis: This is when there is

curvature of the vertebrae the shape of the pelvis(hunch back). The shape and inclination of the pelvis are always affected because the diameters are all reduced and squashed

Effects of abnormal pelvis on labour

If the degree of contraction is sereve elective C/S is carried out. But where there is  minor or moderate contraction of the pelvis, trials of labour may be carried out, as fortunately these women often have small babies (law of compensation is observed).


Normal(gynaecoid) pelvis is ideal for pregnancy and parturition.   However, abnormal pelvis does not favour vaginal delivery and is usually associated with operative delivery. 

We encourage that all women during pregnancy receives adequate nutrition and take their prescribed routine drugs(vitamins and minerals) to ensure that the baby in-utero obtains good supply of nutrients from maternal bloodstream. 

Again, all girl children should be placed on balaced diets, encouraged to engage in moderate and regular exercises and prevent them from engaging in anything capable of causing trauma or injury.