Flashcards in Physiology of 3rd Stage Deck (70)
Define the 3rd stage of labour
- Delivery to expulsion of placenta
- Most dangerous stage
How much has the placental site already diminished by at the start of the 3rd stage?
Describe the process of the placenta detaching
- Placenta becomes compressed
- Blood in intervillous space forced back into spongy layer of decidua basalis
- Retraction of oblique uterine muscles
- With next contraction, distended veins burst and blood seeps between septa of spongy layer and placental surface, stripping it away
- Retroplacental clot forms and shears off villi of spongy layer
- Placenta detaches
What happens when the oblique muscles retract?
- Pressure is exerted on blood vessels to prevent blood draining back into the maternal system
- Blood vessels become tortuous as they are tense and congested with blood
What happens once separation has occurred?
Uterus contracts strongly, forcing the placenta and membranes to fall into lower uterine segment and then the vagina
Give some of the functions of the placenta
What are the 2 sides of the placenta?
1. Amnion - foetal side, inverts during delivery (inside in utero, outside in air)
2. Chorion - maternal side (bloody), inverts during delivery (outside in utero, inside in air)
Describe the umbilical cord
- Outer layer = amnion
- 2 arteries, 1 vein (AVA)
- Surrounded by Wharton's jelly
What forms in the placenta to aid separation?
What does haemostasis mean?
Stopping the flow of blood
How long should the 3rd stage take?
- Usually 5-30 mins but may take up to 1 hour
- Active management = prolonged if not completed within 30 mins
- Physiological management = prolonged if not completed within 60 mins
What is the normal blood flow through a healthy placental site?
What 3 factors control bleeding?
1. Blood vessels
Describe how blood vessels control bleeding
- The tortuous blood vessels intertwine through the oblique uterine muscle fibres
- Retraction of oblique muscles in upper segment results in thickening of muscles
- This exerts pressure on torn vessels, acting as clamps and securing a ligature action
Describe how contractions control bleeding
Presence of vigorous contractions following separation bring the uterine walls into apposition so that further pressure is exerted on the placental site
Describe how coagulation controls bleeding
- Haemostasis is achieved by a transitory activation of coagulation and fibrinolytic systems during and immediately following placental separation
- This is especially active in placental site so clot formation in torn vessels is intensified
- Following separation, placental site is rapidly covered by fibrin mesh, utilising 5-10% of circulating fibrinogen
Give 6 signs of placental separation
1. Contracted uterus
2. No excessive bleeding but a small, fresh blood loss
3. Lengthening of cord
4. Fundus becomes smaller, rounder and more mobile
5. Fundus rises above placental level
6. Placenta is visible at the vagina
What are the 2 types of placental separation?
2. Matthew Duncan
Describe the Shultze separation
- 'Shiny side up'
- Separation begins centrally
- Forms a retroplacental clot
- Foetal surface appears first
- Shorter duration than Duncan
- Less blood loss
- Complete membranes and retroplacental clot visible on examination
Describe the Matthew Duncan separation
- Separation begins at lateral border
- No retroplacental clot
- Maternal surface appears first
- Longer duration than Shultze
- More blood loss
- Ragged membranes visible on examination
What was a major cause of maternal death in the first half of the 1900s?
- PPH (8-22%)
- Decreased to 4-8% by 1978 due to increase availability of blood transfusions, improved nutrition and antenatal care
When was the first routine use of ergometrine?
0.5mg in 1951
What became the drug of choice in the 1960s?
Describe physiological management of the 3rd stage
- Minimal intervention, no drugs
- No cord clamping until after placenta delivery/ cord pulsation has ceased
- Placenta and membranes delivered by maternal effort, guided by gravity
- Encouragement very important
Why would an oxytocic agent be administered in physiological management?
- Uterine tone is poor
- Mother's condition deteriorates
- Mother requests it
What helps with physiological management?
BF as it results in reflux release of oxytocin which encourages the uterus to contract
Describe active management
- Routine administration of uterotonic drugs
- Cord clamping shortly after placenta delivery
- Use of CCT
What is CCT?
Controlled Cord Traction
- Gently pull on umbilical cord and push uterus with each contraction until placenta is delivered (counter traction)
- Designed to enhance normal physiological process
- Incorporated in active management
- Reduces time in 3rd stage to reduce blood loss