ASYNCLITISM

During engagement of the head of fetus into the pelvic inlet brim, the sagittal suture of the fetal head does not correspond with the transverse diameter of the inlet.

So, there is deflection of the head in relation to the pelvis, i.e. head is tilted to one side of the pelvic wall. Such deflection is known as asynclitism.

2 types : 1. Posterior asynclitism

               2. Anterior asynclitism

Posterior asynclitism : When the sagittal suture lies anteriorly ( near to symphysis pubis) , the posterior parietal part becomes the leading presenting part and is known as posterior asynclitism. This most frequently occur in primigravida.

What does posterior parietal part means? – it means that when the sagittal suture lies more anterior , then  most of the parietal bone of fetus head projects out as presenting part is near the sacrum (i.e. posterior region of pelvis) .

 If the words play a confusing note let we understand through a diagram.

Anterior asynclitism : When the sagittal suture lies more posteriorly ( closer to sacrum) , the anterior parietal part becomes the leading part of presentation and is known as anterior asynclitism. Commonly found in multiparae.

Normally this movement occurs during early phase of labour. This movement favours the head entry into the pelvic brim ( inlet ) by lateral flexion. For example, in posterior asynclitism , posterior lateral flexion of the head occurs so that the anterior parietal bone glides the symphysis pubis and enters the inlet.

After this movement, synclitism occurs in 25% of cases. In others mild asynclitism is not a serious issue but severe asynclitism describes cephalopelvic disproportion.