Describe the stages, mechanism of labour, and management of the three stages.

Definition

Labour is the series of events by which the products of conception are expelled from the uterus after the period of viability. Normal labour (eutocia) is one that begins spontaneously at term (37–42 weeks) with the fetus presenting by the vertex, is completed vaginally without undue prolongation or complications and leaves the mother and baby in good condition.

Stages of Normal Labour

Stages of Labour

• First stage — from the onset of true labour pains to full dilatation of the cervix (10 cm); it has a latent phase (up to ~4 cm, slow) and an active phase (rapid dilatation). It lasts about 12 hours in a primigravida and 6 hours in a multigravida.
• Second stage — from full dilatation to the delivery of the baby (≈ 1–2 hours in a primi, ½ hour in a multi); it has a propulsive and an expulsive (bearing-down) phase.
• Third stage — from delivery of the baby to expulsion of the placenta and membranes (≈ 5–15 min).
• Fourth stage — the first hour after delivery of the placenta, during which the mother is observed for haemorrhage.

Mechanism of Labour (in Left Occipito-anterior Position)

The series of passive movements undergone by the head and trunk to negotiate the birth canal — the cardinal movements:

• Engagement — the biparietal diameter passes the pelvic inlet.
• Descent — continuous, brought about by uterine contractions and maternal effort.
• Flexion — the chin approaches the chest, presenting the smallest (suboccipito-bregmatic) diameter.
• Internal rotation — the occiput rotates 1/8 of a circle forwards to lie behind the symphysis pubis.
• Crowning and extension — the head, born by extension, distends the vulva (the occiput pivots under the symphysis).
• Restitution — the head untwists to correct the neck torsion (occiput turns to its original side).
• External rotation — accompanies internal rotation of the shoulders to the antero-posterior diameter.
• Expulsion — the anterior shoulder slips under the pubis, then the posterior shoulder and the rest of the body are delivered.

Management of Labour

First stage

• Reassurance, light diet/fluids, and ambulation in early labour; record observations on a partogram.
• Monitor the fetal heart (every 30 min, after a contraction), maternal pulse/BP/temperature, and contractions; assess cervical dilatation and descent by periodic examination.
• Keep the bladder empty; avoid routine early amniotomy. Provide analgesia as required (epidural).

Second stage

• Encourage bearing-down only with full dilatation; conduct delivery with strict asepsis.
• Support the perineum and control the delivery of the head to prevent tears; perform an episiotomy only if indicated; check for a cord round the neck.
• Deliver the shoulders and body, note the time of birth, and place the baby for immediate care and delayed cord clamping.

Third stage

• Active management — prophylactic oxytocin 10 IU IM with delivery of the anterior shoulder, controlled cord traction with suprapubic counter-traction, and uterine massage after the placenta delivers.
• Examine the placenta and membranes for completeness, inspect the genital tract for tears and repair them, and estimate blood loss.

Fourth stage

Observe the pulse, blood pressure, uterine tone and vaginal bleeding for at least one hour to detect early postpartum haemorrhage; encourage early breastfeeding and skin-to-skin contact.

The partogram plots cervical dilatation against time. The alert line represents the expected rate of progress in the active phase (about 1 cm per hour), and the action line lies four hours to its right. If the patient's progress crosses the alert line, labour is progressing poorly and she should be reassessed and, if necessary, transferred to a unit with emergency obstetric care; crossing the action line demands intervention — which is how the partogram prevents obstructed labour and uterine rupture.

WHY Labour Is Divided Into Stages and Plotted on a Partogram

Understanding why labour is divided into stages, and why progress is plotted rather than merely observed, explains the whole of intrapartum care. The stages mark physiologically distinct processes with different risks: the first stage (onset to full dilatation) is about effacement and dilatation of the cervix; the second (full dilatation to delivery) is about descent and expulsion, and is when fetal hypoxia is most likely; the third (delivery of the placenta) is when the mother is at greatest risk of haemorrhage. The partogram then turns monitoring into a decision tool. By plotting cervical dilatation against time, with an alert line (the expected 1 cm per hour of the active phase) and an action line four hours to its right, it makes the abstract idea of 'poor progress' visible at a glance. Crossing the alert line warns that progress is slow — prompting reassessment and, in a peripheral unit, transfer to a facility with emergency obstetric care; crossing the action line demands intervention (augmentation or caesarean). Its great achievement is the prevention of obstructed labour and its terrible sequelae — uterine rupture, obstetric fistula and fetal death.

WHY the Mechanism of Labour Is a Sequence of Adaptations

A concept that makes normal labour intelligible is why the fetus must perform a precise series of movements to be born. The problem is geometric: the fetal head is not round, and the maternal pelvis is not a straight tube — its inlet is widest transversely, while its outlet is widest antero-posteriorly. The head must therefore continually adjust its orientation, presenting its smallest diameters to each successive plane. Hence the classical sequence: engagement and descent; flexion (chin to chest, converting the presenting diameter from the large occipito-frontal, 11.5 cm, to the small suboccipito-bregmatic, 9.5 cm — the single most important movement); internal rotation (the occiput turns anteriorly to fit the AP outlet); extension (the head pivots under the pubic symphysis and is born); restitution and external rotation (the head untwists as the shoulders rotate); and finally expulsion of the shoulders and body. Understanding that each movement solves a specific mismatch between head and pelvis explains why the mechanism is invariable, why deflexion (as in the occipito-posterior position) presents a larger diameter and prolongs labour, and why the mechanism is the key to every malposition.

• Labour: stage 1 (onset to full dilatation), stage 2 (full dilatation to delivery), stage 3 (delivery of the placenta), stage 4 (first hour — watch for PPH).
• Mechanism: engagement/descent → flexion → internal rotation → extension → restitution/external rotation → expulsion.
• Flexion is crucial — it converts the presenting diameter to the smallest (suboccipito-bregmatic, 9.5 cm).
• The partogram plots dilatation against time with alert and action lines — crossing them prompts reassessment and intervention.
• It prevents obstructed labour, uterine rupture, fistula and fetal death — recommended by the WHO for every labour.