Physiology Of The Third Stage Of Labour

Question 1

What is the third stage of labour?

Answer 1

• it is the period from the birth of the baby through to the delivery of the placenta and membranes and ends with the control of bleeding

Question 2

Describe the separation and descent of the placenta

Answer 2

• due to retraction of the uterus by the beginning of the third stage the placental site has already reduced in area by about 75%
• as this occurs the placenta becomes compressed and the blood in the intervillous spaces is forced back into the spongy layer of the decidua basalis
• retraction of the oblique uterine muscle fibres exerts pressure on the blood vessels so that blood does not drain back into the maternal system
• the vessels during this process became tense and congested
• with the next contraction the distended veins burst and a small amount of blood seeps in between the thin septa of the spongy layer and the placental surface stripping it from its attachment
• as the surface area for placental attachment reduces the placenta begins to detach from the uterine wall

Question 3

What happens after separation has occurred?

Answer 3

• the uterus contracts strongly, forcing placenta and membranes to fall into the lower uterine segment and finally into the vagina

Question 4

What are the signs of placental separation?

Answer 4

• gush of blood
• lengthening of the umbilical cord
• fundus rises and becomes spherical

Question 4

Describe the different methods of Haemostasis

Answer 4

• at placental separation blood low has to be arrested swiftly see serious haemorrhage can occur
• retraction of the oblique uterine muscle fibres in the upper uterine segment through which the tortuous blood vessels intertwine
  - -> the resultant thickening of the muscles exerts pressure on the torn vessels, acting as clamps and preventing haemorrhage
• 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
  - -> there is a temporary activation of the coagulation and fibrinolytic systems during and immediately following placental separation
  - -> it is believed that this protective response is especially active at the placental site so that clot formation in the torn vessels is intensified
  - -> following separation, the placental site is rapidly covered by a fibrin mesh utilizing 5-10% of circulating fibrinogen
• breastfeeding
  - -> the release of oxytocin from the posterior pituitary in response to skin-to-skin contact between mother and baby and the baby’s nuzzling at the breast causes uterine contractions

Question 5

Describe physiological management of the third stage (expectant management)

Answer 5

• in expectant management, the normal, physiological mechanisms of labour are supported and no routine actions are carried out
• it’s important for the midwife to maintain a calm, quiet and warm environment, and encourage skin to skin contact as breastfeeding will stimulate oxytocin release and may shorten the third stage
• maintain the woman is in a comfortable, semi-upright position to encourage placental separation by maintaining a gentle downward weight
• look for signs of separation
• gravity should be used during the birth of the placenta by encouraging a truly upright position (sitting on a birthing stool, standing up, sitting on the toilet, kneeling upright over a bedpan)
• maternal effort can be used to expedite expulsion and most women will push the placenta out as soon as they feel pressure with little effort
• the cord should be left unclamped until pulsation ceases or until after the birth of the placenta
• this spontaneous process can take anywhere from 10mins to 1 hour to complete

Question 6

Describe active management of the third stage of labour

Answer 6

• it usually includes the routine prophylactic administration of a uterotonic agent either intravenously or intramuscularly as a precautionary measure of reducing the risk of pph
• it is usually 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

Question 7

What are uterotonics and what are the ones commonly used in practice?

Answer 7

• they are drugs that stimulate the smooth muscle of the uterus to contract
• they be administered with crowning of the baby’s head, at the birth of the anterior shoulder, after the birth of the baby but prior to placental expulsion or following the birth or delivery of the placenta and membranes
• oxytocin
  - -> synthetic form of the natural oxytocin produced by the posterior pituitary
  - -> can be administered as an intravenous and or intramuscular injection
  - -> research suggests it is better to use oxytocin rather than drugs containing ergometrine due to the side effects
• syntometrine (ergometrine and oxytocin)
  - -> 1ml ampoule contains 5iu of oxytocin and 0.5mg ergometrine and is administered by IM injection
  - -> the oxytocin acts within 2 1/2 minutes and the ergometrine within 6-7mins
  - -> their combined action results in a rapid uterine contraction enhanced by a stronger, more sustained contraction lasting several hours
  - -> can be associated with side effects such as elevation of blood pressure, nausea and vomiting
  - -> no more than two doses of ergometrine 0.5mg should be given
• ergometrine
  - -> often used to treat PPH rather than a prophylactic drug
  - -> can cause headaches, nausea and vomiting and increased blood pressure and is contraindicated where there is a history of hypertensive disorder or cardiac disease

Question 8

What are the advantages of delayed cord clamping?

Answer 8

• even in active management no action to cut and clamp the cord should be taken until cord pulsation ceases
• ensures full transfusion on placental blood to the newborn, up to 30-40% of the circulating volume

Question 9

Describe the process of controlled cord traction (CCT)

Answer 9

• before preceding with CCT the midwife should check
  - -> that a uterotonic drug has been administered
  - -> that is has been given time to act
  - -> that the uterus is well contracted
  - -> that counter-traction is applied
  - -> that signs of placental separation and descent are present
• once the uterus is found to be contracted one hand is placed above the level of the symphysis pubis with the palm facing towards the umbilicus, exerting pressure in an upwards direction (counter-traction)
• the other hand firmly grasping the cord applies traction in a downward and backward direction following the line of the birth canal
• some resistance may be felt but it is important to apply steady tension by pulling the cord firmly and maintaining the pressure
• the aim is to compete the action as one, continuous, smooth controlled movement
• if the manoeuvre is not immediately successful there should be a pause before the uterine contraction is again checked and a further attempt is made
• once the placenta is visible it may be cupped in the hands to ease pressure on the friable membranes
• a gentle upward and downward movement or twisting action will help to coax out the membranes and increase the chances of delivering them intact

Question 10

What is the evidence for active versus expectant management?

Answer 10

• there is an increasing amount of research that suggests that the prophylactic administration of a uterotonic significantly reduces the risk of PPH, results in a lower mean blood loss, fewer blood transfusions are required and there is a reduced need for therapeutic uterotonics
• however women who are ‘low risk’ should still be given the option of expectant management

Question 11

What are the two different types of placental expulsion?

Answer 11

• Schultz method
  
  • -> fundal placenta
  • -> if separation begins centrally a retroplacental clot is formed
  • -> this further aids separation by exerting pressure at the midpoint of placental attachment so that the increased weight helps to strip the adherent lateral borders and peel the membranes off the uterine wall so that the clot formed becomes enclosed in a membraneous bag as the placenta descends
  • -> origin of cord appears at vulva
  • -> followed by fetal surface
  • -> associated with more complete shearing of both placenta and membranes and less fluid blood loss
• Matthews - Duncan method
  
  • -> lateral placenta
  • -> edge of placenta slides out
  • -> followed by rest of maternal side, cord and membranes
  • -> origin of cord not usually seen until placenta is moved
  • -> associated with ragged, incomplete expulsion of membranes and a higher fluid blood loss

After delivery blood loss should be estimated an placenta examined