maternal pelvis and fetal skull

Objectives of this lecture
1- Introduction to normal labour and vaginal delivery passages, passenger, and power.
2- The student should know the types of female pelvis.
3- understand the importance of the dimensions of the bony pelvis of the pregnant woman in determining the progress of labour and the mode of delivery.
4- What are the methods for assessment of pelvic dimensions.
5- Know the dimensions of the fetal skull.
6- Understand how the attitude of the fetal head effect these dimensions.
Labour can be defined as the process by which regular painful contractions bring about effacement and dilatation of the cervix and descent of the presenting part, leading to expulsion of the fetus and the placenta from the mother.
A doctor or midwife who manages labour must be aware of the normal anatomy and physiology of the mother and fetus, what distinguishes an abnormal from a normal labour, and when it is appropriate to intervene
Pelvic diameters:These represent the space available for the fetal head when it passes through the pelvis during labour
the obstetric conjugate of the pelvic inlet: 11 cm
the bispinous diameter: 10.5 cm in the midcavity.
the bituberous diameter 11 cm in the pelvic outlet
the curve and length of the sacrum
and finally the subpubic angle
Clinical pelvimetry
1- The diameters that can be assessed clinically are: the obstetric conjugate of the inlet
2- assess the curvature of the sacrum
3- Then the midpelvis is assessed but it is difficult to do it clinically unless the pelvic side walls are apparently convergent which indicate narrow pelvic cavity the bispinous dimension also can be assessed
4- assessment of the outlet
Dimensions of the fetal skull
The fetal head is the largest and the least compressible part of the fetus
The fetal skull consists of a base and a vault (cranium) which consists of the occipital, parietal, frontal and temporal bones