Asynclitism is when the baby’s head is moving through the pelvis ‘tipped’ to one side. This is usually diagnosed by a vaginal examination in labour. However, asynclitism is rarely caused by the baby having his/her head tilted to one side and rarely a real problem. Instead, like the anterior lip, it is a normal part of the physiological process of birth.
Disclaimer: Routine vaginal examination has NO place during a physiological birth. Unfortunately vaginal examinations continue to be commonly used to determine progress despite the lack of evidence supporting this invasive intervention. In addition, most women do not experience a physiological birth and instead have their labour induced or augmented. Once an intervention is implemented it’s effects need to be monitored ie. assessment of cervical dilation. Therefore, the following explains what is felt during an examination in relation to what is happening as the baby descends and rotates through the pelvis.
Asynclitism: normal birth physiology
The baby enters the pelvis through the brim/inlet. The easiest way to do this is with the head in the transverse position (facing sideways to mother). However, the baby is not lying in a perfecting vertical position. The woman’s pelvis is tilted and her uterus/baby are also sticking out at an angle – check out a pregnant woman for confirmation. If at this point in the birth process you put your fingers into her vagina, you will feel the side of the baby’s head near the symphysis pubis. If you dig further you will feel the saggital suture towards the back of the pelvis. The baby’s head is not tilted… it is perfectly aligned with the baby and the pelvis.
Once the baby has descended into the cavity/mid-pelvis he will use the space and the counter pressure of the pelvic floor (unless the muscle tone is reduced by an epidural) to rotate an anterior position (facing towards mother’s back) to fit the shape of the pelvic outlet. It is not until the baby has made this rotation that you will feel the centre of the head in the middle of the pelvis. If the baby’s head is well flexed, you will also be able to feel the occiput, the posterior fontanelle and the lambdoidal suture (I love that word – lambdoidal).
Asynclitism: a variation or complication
Asynclitism is a normal part of the birth process. When it is caused by a tipped head it can alter the pattern of labour and may require additional work and support. It can be difficult to work out which type of asynclitism is happening via a vaginal examination (normal or a tilted head). Therefore it is best to keep fingers out of the vagina and focus on the woman and what she does or does not need from you.
I would love to hear your experiences of asynclitism.