CHAPTER 9

FETOPELVIC RELATIONSHIP

​

INTRODUCTION

Fetal orientation with respect to the human pelvis is described in terms of fetal lie, presentation, attitude, position.

LIE

It is the relationship between the long axis of both the fetus and the uterus. Lie can be longitudinal, transverse or oblique

PRESENTATION

It is defined as the part of the fetus that lies over the pelvic outlet and ready to come out first through the canal during delivery.

The presentation can be of three types :

• Cephalic
• Podalic or breech
• Shoulder

Diagrammatic representation of the fetal presentation in the uterus

Presenting Part

It is the part of the fetus felt first during vaginal examination or which overlies the internal os.

For example:

• In the cephalic presentation, the presenting part may be the vertex, brow or face depending on the degree of head flexion.
• In breech presentation, the presenting part may be fetal legs.

• Frank breech, in which the baby is positioned with its legs pointed upward, knee straight, and feet close to its ears. This is the most common kind of breech.
• A footing breech occurs when one or both of the baby’s feet are born first rather than the pelvis. Babies born early or before their due date are more likely to experience this.
• A complete breech (Flexed) is when the infant looks like it is sitting cross-legged with its legs bent at the hips and knees.

Presenting part in legs, footling (or presence of the foot), breech presentation

Showing the shoulder and other presentations

ATTITUDE

The relation of the different parts of the fetal body with one another is known as attitude. Normal fetal attitude is flexion when the head is tucked down to the chest with its arms and legs drawn in towards center of chest. The flexion depends on the amount of amniotic fluid.

Flexion

The head flexed over the chest, arms and legs flexed in front of the body and the back curved forward.

Presenting part and fetal attitude in vertex presentation

DENOMINATOR

An arbitrary bony fixed point on the presenting part which comes in relation with the various quadrants of maternal pelvis. It is used to describe the position of the fetus within the uterus. For example:

• In vertex, the denominator is occiput
• In face, mentum
• In brow, frontal eminence
• In breech, sacrum
• In the shoulder, acromian process

Position

It is the relationship of the denominator to the various quadrants of the maternal pelvis. There are 8 quadrants present with an angle of 45 degrees.

Different fetal positions within the uterus

Why is longitudinal lie and cephalic presentation more common at term?

When the fetus is in the attitude of good flexion, it has the shape of an ovoid. The uterus also has the same shape. Thus the long axis of the fetal ovoid can be accommodated in the long axis of the uterine ovoid. Hence longitudinal lie is more common. The head being the heavier part comes to the lower pole due to gravity. This leads to cephalic presentation.