Chapter 19 The Third Stage of Labour

Physiological processes

During the third stage of labour, separation and expulsion of the placenta and membranes occur as the result of an interplay of mechanical and haemostatic factors. The time at which the placenta actually separates from the uterine wall can vary. It may shear off during the final expulsive contractions accompanying the birth of the baby or remain adherent for some considerable time. The third stage usually lasts between 5 and 15 minutes, but any period up to 1 hour may be considered to be within normal limits.

Separation and descent of the placenta

Mechanical factors (Fig. 19.1)

Separation usually begins centrally so that a retroplacental clot is formed (Fig. 19.2). Two methods of separation are described:

Schultze (Fig. 19.3A).

Matthews Duncan (Fig. 19.3B).

Fig. 19.1 The placental site during separation. (A) Uterus and placenta before separation. (B) Separation begins. (C) Separation is almost complete.

Fig. 19.2 The mechanism of placental separation. (A) Uterine wall is partially retracted, but not sufficiently to cause placental separation. (B) Further contraction and retraction thicken the uterine wall, reduce the placental site and aid placental separation. (C) Complete separation and formation of the retroplacental clot. Note: the thin lower segment has collapsed like a concertina following the birth of the baby.

Fig. 19.3 Expulsion of the placenta. (A) Schultze method. (B) Matthews Duncan method.

Once separation has occurred, the uterus contracts strongly, forcing the placenta and membranes to fall into the lower uterine segment and finally into the vagina.

Haemostasis

The three factors that are critical to control of bleeding are the following:

Retraction of the oblique uterine muscle fibres in the upper uterine segment through which the tortuous blood vessels intertwine.

The presence of vigorous uterine contraction following separation – this brings the walls into apposition so that further pressure is exerted on the placental site.

The achievement of haemostasis – following separation, the placental site is rapidly covered by a fibrin mesh utilising 5–10% of the circulating fibrinogen.

Management of the third stage

Uterotonics or uterotonic agents

These are drugs (e.g. Syntometrine, Syntocinon, ergometrine and prostaglandins) that stimulate the smooth muscle of the uterus to contract. They may be administered with crowning of the baby’s head, at the time of birth of the anterior shoulder of the baby, at the end of the second stage of labour or following the delivery of the placenta.

Information related to the best available research information on the use of uterotonic drugs during the third stage of labour should be provided in an objective manner.

Expectant or physiological management

In the event of expectant management:

routine administration of the uterotonic drug is withheld

the umbilical cord is left unclamped until cord pulsation has ceased or the mother requests it to be clamped, or both

the placenta is expelled by use of gravity and maternal effort.

With this approach, therapeutic uterotonic administration would be administered either to stop bleeding once it has occurred or to maintain the uterus in a contracted state when there are indications that excessive bleeding is likely to occur.

Active management

This is a policy whereby prophylactic administration of a uterotonic is applied, regardless of the assessed obstetric risk status of the woman. This is undertaken in conjunction with clamping of the umbilical cord shortly after birth of the baby and delivery of the placenta by the use of controlled cord traction. One of the following uterotonic drugs is usually used:

ergometrine

oxytocin

combined ergometrine and oxytocin.

Intravenous ergometrine 0.25 mg

This drug acts within 45 seconds; therefore it is particularly useful in securing a rapid contraction where hypotonic uterine action results in haemorrhage.

If a doctor is not present in such an emergency, a midwife may give the injection.

Combined ergometrine and oxytocin

(A commonly used brand is Syntometrine.)

A 1-ml ampoule contains 5 IU of oxytocin and 0.5 mg ergometrine and is administered by intramuscular injection.

The oxytocin acts within 2.5 minutes, and the ergometrine within 6–7 minutes.

Their combined action results in a rapid uterine contraction enhanced by a stronger, more sustained contraction lasting several hours.

Administered, normally, at birth of the anterior shoulder.

Caution. No more than two doses of ergometrine 0.5 mg should be given, as it can cause headache, nausea and an increase in blood pressure; it is normally contraindicated where there is a history of hypertensive or cardiac disease.

Oxytocin

(A commonly used brand is Syntocinon.)

Oxytocin can be administered as both an intravenous and an intramuscular injection. However, an intravenous bolus of oxytocin can cause profound, fatal hypotension, especially in the presence of cardiovascular compromise.

No more than 5 IU should be given by slow intravenous injection.

Clamping of the umbilical cord

This may have been carried out during birth of the baby if the cord was tightly around the neck. Early clamping is carried out in the first 1–3 minutes immediately after birth, regardless of whether cord pulsation has ceased.

Proponents of late clamping suggest that no action be taken until cord pulsation ceases or the placenta has been completely delivered, thus allowing the physiological processes to take place without intervention.

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Related posts:

1. The Placenta
2. Prolonged Pregnancy and Disorders of Uterine Action
3. Obstetric Emergencies
4. Problems of Pregnancy

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