Physiology of 3rd Stage Flashcards
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?
75%
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
- Respiration
- Nutrition
- Storage
- Excretion
- Protection
- Endocrine
What are the 2 sides of the placenta?
- Amnion - foetal side, inverts during delivery (inside in utero, outside in air)
- 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?
Retroplacental clot
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?
500-800ml/min
What 3 factors control bleeding?
- Blood vessels
- Contractions
- Coagulation
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
- Contracted uterus
- No excessive bleeding but a small, fresh blood loss
- Lengthening of cord
- Fundus becomes smaller, rounder and more mobile
- Fundus rises above placental level
- Placenta is visible at the vagina
What are the 2 types of placental separation?
- Shultze
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?
Syntometrine
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
Describe CCT
- 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
What is a cord prolapse?
Umbilical cord comes out with/ before the presenting part (before baby is delivered)
What should be checked prior to CCT?
- Has oxytocic drug been given?
- Has time been allowed for it to act?
- Is uterus well contracted?
- Are there signs of placental separation and descent?
What should not be done during CCT?
- Do not apply traction to cord if placenta is not separated - risk of uterine inversion
- No ‘fundal fiddling’ (repeatedly palpating uterus) as this will cause the uterus to relax
What are the 3 main drugs used?
- Syntocinon
- Ergometrine
- Syntometrine
Describe syntocinon
- Synthesised oxytocin
- Prevents and treats haemorrhage during 3rd stage
- Also used for induction and augmentation
- Must not be used for women with raised BP
What is the normal dosage for syntocinon?
- 40 units in 500ml of N/Saline via Hartmann’s IV
OR - 5 units of oxytocin (slow bolus IV) - administered slowly due to profound and potentially fatal hypotensive side effects
Describe ergometrine
- Oxytocic drug given at end of labour
- Controls bleeding
- Causes strong, sustained contractions
- Acts within 6-7 mins (IM)
- Contra-indicated if there is a history of hypertensive or cardiac disease
- Used IV if haemorrhage due to hypotonic uterine action as it secures rapid contraction in 45 seconds
What is the normal dosage of ergometrine?
500mg in 1ml (IM) with oxytocin 5 units
Describe syntometrine
- Syntocinon and ergometrine mixed
- Oxytocin stimulates contractions and ergometrine sustains them
- Effects last for several hours
- Effective in 2-3 mins when given IM
- Side effects = raised BP and vomiting
What is the normal dosage for syntometrine?
Oxytocin = 5 IU in a 1ml ampoule Ergometrine = 0.5mg in a 1ml ampoule
When does administration of a uterotonic drug usually take place?
As the anterior shoulder of the baby is born
What should be done on completion of the 3rd stage
- Estimation of blood loos
- Examination of placenta
- Examination of perineum
What are the common volumes of blood lost?
- Normal delivery = up to 250ml is acceptable
- Woman sitting in pool of blood = 250-300ml
- Blood spilling off bed = 500ml (risk of haemorrhage)
What observations should be done following 3rd stage?
- If there is excessive bleeding but uterus has contracted well, it may be coming from somewhere else (e.g. perineal/ cervical tear)
- Never leave mother and baby on their own for first few hours (e.g. risk of mother fainting)
- After placenta is delivered and everything is cleared up, check perineum again for blood loss before leaving
What should be checked on the placenta?
- Hold up by cord to check membranes for completeness
- Check number of vessels
- Check for succenturiate lobe
- Strip back amnion from chorion to cord to ensure both are present
- Examine chorion
- Estimate blood loss
- Record findings
What may the absence of an artery in the umbilical cord be associated with?
Renal disease in the baby
What is a succenturiate lobe?
- Check for vessels around edge of placenta
- Small extra lobe in addition to main placenta and attached via blood vessels
What should be checked on the chorion?
- Check all lobes are present
Check for: - Infarcts (dead cells - fatty deposits cause placenta to break away from uterus lining)
- Calcification (hardened areas caused by accumulation of calcium salts)
- Missing pieces
What should be done if part of the placenta/ membranes are missing?
- Woman is given antibiotics
- Blood clots should be monitored by midwife until all has come out
What is a bipartite placenta?
- 2 complete and separate parts with a cord leaving each part which join a short distance from the placenta
- Placenta in twins are separate with 2 separate cords
What is a battledore insertion?
Cord is attached at the very edge of the placenta
What is a velamentous insertion?
Cord is inserted away from the edge of the placenta in the membranes
What are the 3 main complications that may occur in 3rd stage?
- PPH - excessive bleeding from genital tract at any time after baby’s birth up to 24 hours
- Blood Loss - reaching 500ml must be treated as a PPH
- Secondary PPH - abnormal or excessive bleeding from genital tract occurring between 24 hours and 12 weeks postnatally
Give 8 reasons that a PPH might occur?
- Atonic uterus
- Retained placenta
- Trauma
- Blood coagulation disorder
- Previous history of PPH/ retained placenta
- High parity
- Anaemia
- HIV/AIDS
What is an atonic uterus?
Failure of the myometrium at the placental site to contract and retract and to compress torn blood vessels to control blood loss by living ligature action
What are the 3 principles of care in PPH?
- Call for help
- Stop the bleeding
- Resuscitate the mother
If the uterus is firmly contracted, how should bleeding be stopped?
- Lower genital injury = apply pressure and repair the wound
- Ruptured uterus = laparotomy (repair the tear) or hysterectomy
- Clotting disorder?
If uterus is atonic, how should bleeding be stopped?
- Rub up a contraction
- Give oxytocin - put baby to breast, give ergometrine (0.5mg IV) or syntocinon (4.0 u/L IV)
- Empty bladder (bedpan/ catheter)
- Empty the uterus
How should the uterus be emptied if the placenta has been delivered?
Expel clots; if this fails to arrest bleeding, apply bimanual compression and perform hysterectomy
How should the uterus be emptied if the placenta is undelivered but separated?
- Grasp and remove if in vagina
- Use CCT if in lower uterine segment
- If this fails to arrest bleeding, apply bimanual compression and perform hysterectomy
How should the uterus be emptied if the placenta is undelivered and unseparated (retained)?
- Attempt manual removal
- Unsuccessful = placenta accreta
- Give antibiotics or perform hysterectomy
What is placenta accreta?
Blood vessels and other parts of the placenta grow too deeply into uterine wall to be removed
How should the mother be resuscitated?
- Restore circulation
- Assess postnatal Hb levels
- Correct as appropriate
How is bimanual compression applied?
- Apply pressure to placental site
- Insert fingers of one hand into vagina like a cone
- Form hand into fist and place into anterior vaginal fornix
- Place other hand behind uterus abdominally, fingers pointed towards cervix
- Bring uterus forward and compress between palm of abdominal hand and fist in vagina
What are the pregnancy related causes of an atonic uterus?
- Multiple pregnancies
- Polyhydramnios - causes overdistension of the uterine muscle
What placental conditions may cause an atonic uterus?
- Placenta praevia as it partly/wholly lies in lower segment where thinner muscle layer contains few oblique fibres, resulting in poor control of bleeding
- Placental abruption as blood may have seeped between muscle fibres, interfering with effective muscle action - severe cases result in a Couvelaire uterus
What sort of labour may cause an atonic uterus?
Precipitate labour (very fast) and prolonged labour resulting in uterine inertia (absence of effective contractions) resulting from maternal exhaustion/ sluggishness
What other factors may cause an atonic uterus?
- Incomplete retained placental fragments/ membranes and cotyledon
- Full bladder interferes with uterine action
- General anaesthesia may cause uterine relaxation
What are cotyledon?
Separations of the placenta
When would a uterus be described as ‘boggy’?
On palpation, an enlarged uterus filling with blood/ clots feels soft and distended and lacking tone
When would cord blood sampling usually be taken?
When atypical maternal antibodies have been found during antenatal screening tests
