Third Stage of Labour

Third stage of labour

 

Mechanism of placental seperation

Separation of the placenta is brought about by contraction and separation retraction retraction of the myometrium which thicken the uterine wall and reduces the size of the placental area. As the placental area becomes smaller, the placenta begins to tear off the uterine wall because, unlike the uterus, it is not elastic and cannot contract and retract. At the area of separation a clot forms. This clot, known as a retroplacental clot, collects between the decidua and the placenta and further promotes separation. Subsequent uterine contractions completely detach the placenta from the uterine wall and it descends into the lower uterine segment and then into the vagina

from where it is expelled.

There are two methods of separation of the placenta which have been described by Schultze and Matthews Duncan. These methods are not under the control of the birth attendant.

·   The Schultze method is said to be the more common. The placenta detaches from a central point and slips down into the vagina through the hole in the amniotic sac; the fetal surface appears at the vulva, with the membranes trailing behind like an inverted umbrella as they are peeled off the uterine wall. The maternal surface of the placenta is not seen, and any blood clot is inside the inverted sac.

·     In the Matthews Duncan method, the placenta slides down sideways and comes through the vulva with the lateral border first, like a button through a buttonhole. The maternal surface is seen, and the blood escapes as it is not inside the sac. It is more likely that parts of the membranes will be left behind with the Matthews Duncan method, as they may not be peeled off as completely as in the Schultze method. The Matthews Duncan method may be associated with a placenta lying lower in the uterus. The process of separation takes longer and blood loss is greater (because there are fewer oblique fibres in the lower segment).

Signs of placental separation

1. The fundus feels hard and globular, and rises abdominally to the level of the umbilicus.
2. The cord lengthens at the vulva.
3. A trickle of blood appears when the placenta separates.

Control of bleeding

About 500–800 ml of blood flow through the placental site each minute. If there was no mechanism after delivery to control the bleeding, this is how quickly the woman would lose blood. She would bleed to death in a matter of minutes. The contraction and retraction of the uterine muscle that bring about separation of the placenta also compress the blood vessels strongly and thus control the bleeding. This is possible because of the presence of oblique muscle fibres in the upper uterine segment. Later, blood clots also form in the torn blood vessels at the placental site, and these too will stop the blood flow. A full bladder or anything left behind in the uterus after delivery such as placental tissue, membranes or blood clots, interfere with the ability of the uterus to contract and will cause the woman to bleed excessively.

Examination of the Placenta and membranes

Appearance of the The placenta is a round, flat mass. The maternal surface is placenta at term bluish–reddish and made up of lobules which are composed of chorionic villi. It is through these villi that the interchange of substances between the fetal and maternal blood takes place. This interchange occurs without mixing of fetal and maternal blood under normal circumstances. The fetal surface is smooth, white and shiny branches of the umbilical vein and arteries can be seen running across the surface to the insertion of the umbilical cord. The fetal surface is covered with the amnion which is continued beyond its outer edge to form the membraneous sac that, together with the chorion, contains the fetus and amniotic fluid.

The umbilical cord extends from the fetal umbilicus to the fetal surface of the placenta. It usually measures approximately 56 cm in length. It carries three vessels, two arteries containing deoxygenated fetal blood going to the placenta, and one vein containing oxygenated blood going back to the fetus. The cord is usually inserted in the centre of the fetal surface of the placenta. Occasionally the cord is inserted into the membranes of the fetal sac some distance from the edge of the placenta. In these cases the umbilical blood vessels run through the membranes between placenta and cord (velamentous insertion). This form of insertion is more dangerous because, when membranes of the fetal sac rupture or when an amniotomy is done, the blood vessels may be damaged and bleeding occurs.

Hold the placenta in the palms of the hands (palms should be kept flat); all the lobules on the maternal side should be present and they should fit together. There should be no irregularities on the margins. If the maternal side is carefully rinsed with water and held to the light, a shiny layer should be seen (the decidua). If it is not intact, it may indicate that some fragments of placenta are left behind. On the fetal side, the membranes should appear complete. Hold the umbilical cord in one hand and let the placenta hang down: check that the membranes are complete, there should be one hole – where the baby came through (if placenta expelled by Matthews Duncan method, the membrane may be torn in more than one place). It also gives you the opportunity to look for free-ending vessels on the membranes which may indicate the presence of an extra lobe of placenta (placenta succenturiata or bipartita) which is left behind in the uterus.

MANAGEMENT OF THE THIRD STAGE OF LABOUR

The third stage of labour is the most dangerous time, because of the risk of bleeding which can be life-threatening.  The active management of the third stage must be carried out correctly, otherwise serious complications may occur such as haemorrhage and/or inversion of the uterus.

Active management:

1. An oxytocic drug (such as oxytocin 10 IU IM or ergometrine 0.2 mg IM) is given after delivery of the baby and immediately after the midwife has palpated the uterus to check that there is not a multiple pregnancy.

2. The cord is clamped and cut, immediately after the drug is given.

3. When the uterus is well contracted it will feel very hard. This should occur 2–3 minutes after the administration of oxytocin. Then controlled cord traction is used  the lateral surface of one hand is placed firmly over the lower segment of the contracted uterus and counter traction is applied while the cord is gently pulled with the other hand until the placenta and membranes are delivered. Steady, sustained cord traction is applied following the curve of the birth canal; this means that at first traction is in a downward direction, then horizontally and finally, when the placenta is visible in the vagina, in an upward direction. If controlled cord traction fails on the first attempt after a minute or two, the midwife should stop traction and wait for the uterus to

contract again before a second attempt. Apply Controlled cord traction - to avoid inversion of the uterus, controlled cord traction should never be applied without counter-traction

4. As the placenta is delivered, it should be caught in both hands at the vulva to prevent the membranes tearing and some being left behind. 

Physiological management:

·         No oxytocics are used before delivery of the placenta.

·         Signs of placental separation are awaited.

·         Delivery of the placenta is by gravity and maternal effort.

·         The cord is clamped after delivery of the placenta (or sometimes when the pulsations have ceased), unless there is a need to clamp and cut the cord for neonatal reasons.m This method should only be used in situations when no oxytocic drugs are available.

·         Once signs of placental separation are visible, check that the uterus is well contracted and, if it is, ask the woman to bear down to push the placenta out.

·         Catch the placenta in both hands as it emerges from the vagina. I

·         f the placenta fails to deliver, check that the bladder is empty and, if not, ask the woman to pass urine, then try again to deliver the placenta with the next uterine contraction.

Choice of oxytocic drugs Oxytocics cause the uterus to contract. They speed up the delivery

of the placenta and lessen the blood loss. The choices are:

A. Oxytocin.

B. Syntometrine.

C. Ergometrine.

A.Oxytocin

Oxytocin is a pituitary (posterior lobe) extract which can be prepared synthetically:

• causes contraction of smooth muscle and therefore has apowerful action on the uterine muscle
• acts within 2½ minutes when given intramuscularly.

Advantages of oxytocin: It has a rapid action and does not cause side effects in most cases. It is also more stable in hot climates.

Disadvantages of oxytocin: It does not have a sustained action.

B. Syntometrine

Syntometrine is a combined preparation, ergometrine and oxytocin which is given by intramuscular injection.

Advantages of syntometrine:

It has the combined effect of the rapid action of oxytocin and the sustained action of ergometrine.

Disadvantages of syntometrine:

There is a greater risk of producing temporary hypertension and vomiting.

C. Ergometrine

Ergometrine is a preparation of ergot which:

• may be given orally, intramuscularly or intravenously. However, oral preparation has been found to be ineffective for active management of the third stage - and should not be used for this purpose
• takes 6–7 minutes to take effect when given intramuscularly, and 45 seconds when given intravenously
• causes marked spasm of the uterus by a series of rapid contractions
• has an effect lasting approximately 2–4 hours.

Advantages of ergometrine:

It is the cheapest of the oxytocic drugs and it has a sustained action.

Disadvantages of ergometrine:

Headache, nausea and vomiting, and hypertension. Ergometrine is therefore definitely contraindicated and should never be given to women with raised blood pressure and/or

cardiac disease. Ergometrine stored at room temperature or exposed to light, may

lose a lot of its potency.

Recommendations for practice

1. The use of oxytocin is recommended. Where this is not available, syntometrine or ergometrine should be used.

2. Preparations containing ergometrine should not be used for women with raised blood pressure or cardiac disease.

3. It is recommended that oxytocics should be stored in a refrigerator at 2–8°C and away from light.

Timing of administration of oxytocic drugs

A. With the crowning of the head.

B. With the birth of the anterior shoulder.

C. After the delivery of the baby when it is confirmed that there is not a second twin.

There is not a great deal of research available on this subject. However, because of the danger of intrauterine asphyxia of an undiagnosed second twin, it makes sense to wait until delivery of the

baby and confirmation that there is not a second twin before giving an oxytocic drug.

Recommendations for practice

1. Give oxytocic drugs after delivery of the baby, when it has been confirmed by abdominal palpation that there is no second twin.
2. Allow time for the oxytocic drug to act and ensure that the uterus is well contracted before applying controlled cord traction.
3. Suckling of the baby at the breast stimulates the natural production of oxytocin. Oxytocin helps the uterus to contract.