Types of pelvis
Classically,pelves have been described as falling into four categories according to the shape of the brim.It is unlikely that women's pelvis is classified in life unless she encounters difficulties in child brith.Of much more importance is the individual woman's pelvic capacity and whether it is adequate for the passage of the child she is carrying.It is common saying that the fetal head is the best pelvimeter.If one of the important measurements is reduced by 1 cm or more from the normal,the pelvis is said to be contracted and may give rise to difficulty in labor or necessitate cesarean section.
The gynaecoid pelvis
This is the ideal pelvis for childbearing.Its main features are the rounded brim,the generous forepelvis,straight side walls,a shallow cavity with a broad,well-curved sacrum,blunt ischial spines,a rounded sciatic notch and a sub-pubic angle of 90 degree.It is found in women of average build and height with a shoe size of 4 or larger.Justo minor pelvis:This pelvis is like a gynaecoid pelvis in miniature.All diameters are reduced but are in proportion.It is normally found in women of small stature,less than 1.5m in height,with small hands and feet,but occasionally found in women of normal stature.The outcome of labor in this situation depends on the fetus.If the fetal size is consistent with the size of the maternal pelvis,normal labor and birth will take place.Often these women have small babies and the outcome is favorable.However,if the fetus is large,a degree of cephalopelvic disproportion will result.The same is true when a malpresentation or malposition of the fetus exists.
The android pelvic
This is so called because it resembles the male pelvis.Its brain is heart shaped with a narrow forepelvis,and has a transverse diameter that is towards the back.The side walls converge,making it a funnel shape with a deep cavity and a straight sacrum.The ischial spines are prominent and the sciatic notch is narrow.The sub-pubic angle is less than 90 degree.It is found in short and heavily built women who have a tendency to be hirsute.This type of pelvis predisposes to an occipitoposterior position of the fetal head and is the least suited to child bearing.The heart shaped brim favors a posterior position of the occiput as a result of insufficient space for the bi parietal diameter in the narrow forepelvis,combined with the fact that the greater space lies in the hind pelvis. Funneling in the cavity may hinder progress in labor.At the pelvis outlet,the prominent ischial spines sometimes prevent complete internal rotation. of the head and the anterposteroir diameter becomes caught on them,causing a deep transverse arrest.
The anthropoid pelvis
This has a long,oval brim in which the anteposterior diameter is longer than the transverse.The side walls diverge and the sacrum is long and deeply concave.The ischial spines are not prominent and the sciatic notch is very wide,as is the sub-pubic angle.Women with this type pf pelivs tend to be tall,with narrow shoulders.Labor does not usually present any difficulties,but a direct occipitoanterior or direct occipitoposterior position id often a feature and the position adopted for engagement may be persist to delivery.
The platypelloid pelvis
This flat pelvis has a kidney-shaped brim in which the anteposterior diameter is reduced and the transverse increased.The side walls diverge,the sacrum is flat and the cavity shallow.The ischial spines are blunt,and the sciatic notch and the sub-pubic angle are both wide.The head must engage with the sagittal suture in the transverse diameter,but usually descends through the cavity without difficulty.Engagement may necessitate lateral tilting of the head,known as asynclitism,in order to allow the bi parietal diameter to pass the narrowest anteoposterior diameter of the brim.