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Introduction

For so long the definition of labour is one that has confused the medical community. There are certain facts about the process that are constant though.

1. The fetus and the placenta are expelled per vaginam.
2. Labour as a means of birthing is a safe process when compared to its surgical counterpart.
3. During the process there are painful, palpable and regular uterine contractions of progressively increasing frequency and intensity.
4. the cervix which is the lowest portion of the uterus (a pear shaped organ whose primary function is to house the developing fetus) gets dilated and effaced.
5. The fetal presenting part (the part of the fetus at the lower segment of the uterus) descends gradually and is delivered

Normally the contractions during labour start at a frequency of one every ten minutes and progressively increases. The contractions of labour is one of the three main signs of labour and is usually accompanied by the drainage of liquor (this is the amniotic fluid that baths the growing fetus) and the passage of show (mucosl plug that covers the cervix), these processes do not come in any particular order.

https://en.m.wikipedia.org/wiki/Childbirth
STAGES OF LABOUR
For the purpose of study in this article we're going to divide labour into three stages that are indistinct.

Stage 1
The main activity of this phase is cervical dilatation. It is in this phase the cervix dilates from a resting state of zero centimetres (cm) to a state of full dilatation at ten cm. This stage is divided also into:
•Latent phase
•Active phase

Latent phase
During this phase the cervix dilates to about 3-4cm. This phase can happen weeks before the onset of labour. The time duration is usually 3-8 hours.

Active phase
This is the time between the latent phase and full cervical dilatation of 10cm. The cervical dilatation happens 1cm/hour. The normal duration for this phase is 2-6hours.

Stage2
This is the period between full cervical dilatation and delivery of the baby or babies. This phase can also be divided into two phases:
•Passive phase
•Active phase

So in medical terms we say

"active phase of the second stage of labour"

Passive phase
In this phase the mother doesn't feel the urge to push, the fetal head is still in the upper pelvic portion.

Active phase
The mother's urge to push comes at this phase also the fetal head is lodged at the lower pelvic portion. At this point the mother is encouraged to push. An examination of the vagina will also help to know when this phase has arrived.

Third stage of labour
This stage happens after delivering the baby or babies. I this phase the placenta (the vascular organ involved with nutrients, oxygen and waste exchange between the mother and the fetus) is delivered either passively (by waiting for it to detach from the uterus) or actively (by applying traction on the umbilical cord). The normal duration is about 30minutes.

The duration of labour
Most women become exhausted as the duration of labour increases also there is risk of fetal hypoxia (lack of oxygen) and subsequently the woman may have to be delivered by caesaeren section. Most authors suggest labour as prolonged when it last more than 8hours (in women who have had multiple pregnancies) and 12hours (in women who have there first pregnancy).

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THE MECHANISM
These are changes in the position of the fetus and movement done by the fetus to navigate the birth canal. It is the relation of the head and body of the fetus the Maternal pelvis during parturition. The mechanism comprises of:
•Engagement
•Descent
•Flexion
•Internal rotation
•Extension
•Restitution
•External rotation
•Delivery of the shoulder and fetal body

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Engagement
The head of the baby enters into the mid pelvic cavity by passing through the transverse pelvic diameter of the upper pelvic passage. Engagement happens when the largest part of the presenting part (the part of the fetus occupying the lowest portion of the uterus) has successfully passed through the upper pelvic opening (inlet). Normally when this occurs only 2/5 of the fetal head I s palpable on abdominal examination.

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Descent
This happens befor the head is flexed in the mid cavity. Descent is usually secondary to uterine contractions and also by pushing (valsalva manoeuvre).

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Flexion
As the fetal head descends into the narrow mid cavity it begins to flex due to pressure by surrounding structures.

Internal rotation
At this point the fetal chin is in contact with the chest, the face is turned to the left. When internal rotation occurs the fetal head is turned to face forward with the face intended to make its way out facing the gulteal region (buttocks). This is so that the widest diameter or the fetal head passes the widest diameter of the lower pelvic opening (pelvic outlet). This is also known as 'face to pubes'.

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Extension
As the fetal head makes its way through the vagina it begins to extend in order to give room for the shoulders to make their way through the bid cavity. The fetal head then distends the vulvar. This is know as crowning

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Restitution
As the head is delivered it relines itself with the shoulder. This slight rotation is known as restitution.

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External rotation
In order to be delivered, the shoulders have to be rotate into the plane of the pelvic outlet. When this occurs the head rotates 1/8th of a circle.

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Delivery of the shoulder and fetal head
When restitution and external rotation happen the shoulder would be ready to be delivered. This process happens without assistance sometimes traction may be needed. After this the rest of the body is delivered with ease.

Conclusion
Labour brings joy and happiness when it is happens safely, the mechanism of labour are important to know when something wrong might happen.

Reference
•Obstetrics for medical students by Akin Agbloola
• Obstetrics by ten teachers
•https://en.m.wikipedia.org/wiki/Childbirth

Thank you for reading