Physiology of labour Flashcards
UNFINISHED. WEEK 2
What does normal labour physiologically include
Regular uterine contractions which stimulate progressive effacement and dialation of the cervix and decent of fetus
Gould 2000
What features does WHO define normal labour as having
-Spontaneous onset between 37 and 42 wks
-Low risk at start and remainder of pregnancy/birth
-Spontaneous birth of bb in vertex presentation
-Mother and bb in good condition after birth
What % of women does the WHO estimate are low risk at the start of labour
70-80%
Whats the 1st stage of labour and how long does it last for primi/multigravidae
The onset of regular uterine contractions, along with effacement and dialation of cervix to full dialation of the os uteri
Primigravidae=12-14hrs
Multigravidae=6-10hrs
Whats the 2nd stage of labour and how long does it last for primi/multigravidae
From full dialation of os uteri to the birth of the baby
Primigravidae=60mins
Multigravidae=30mins
Whats the 3rd stage of labour and how long does it last for primi/multigravidae
From birth of bb to birth of placenta and membranes
Primigravidae=20-30mins or 5-15mins w active management
Multigravidae=20-30mins or 5-15mins w active management
Are decisions about care based on the ‘stages’ model good or bad?
- Decisions about care based on the ‘stages’ model have been
shown to lead to unnecessary intervention with a consequent
increase in maternal and neonatal morbidity (Winter and
Cameron 2006)
What does the fetus determine in pregnancy/labour
- The fetus determines the duration of pregnancy
through the culmination of prelabour physiologic
preparations and signals this readiness to the
mother’s body
What does the mothers physiology determine in pregnancy/labour
The mother’s physiology determines the time of day
that labour commences through day-night (circadian)
rhythms (Buckley 2015)
Just read
- The changes in uterine contractility and cervical
characteristics are processes that occur over a period of
weeks rather than being a sudden event - Winter and Cameron (2006) contend that this supports
the view of labour as part of a continuum
What is the hypothalmus
-Area of the brain that linnks the brain to the endocrine system
-Sits at base of brain and is connected to pituaitary gland by stalk of nerves and BVs
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Where is oxytocin produced, stored and released.
-In the hypothalmus
-Stored and secreted by posterior pituitary gland where its released into blood stream in pulses
What does oxytocin do?
Directly stimulates uterine contractions
Explain significance of oxytocin receptors
-Oxytocin needs to bind to specific receptors in order to trigger contracctions.
-If not enough receptors, or if progesterone or relaxin are too strong the uterus mightnt be able contract properly
Where are oxytocin receptors located?
Uterine smooth muscle and myoepithelial cells that surround mammary alveoli
Top of uterus/fundus
What is a contraction
-The process in which a muscle becomes shorter + tighter
-When muscles of uterus tense+relax, passing in waves from top, inwards then downwards
-Feel like a v strong menstrual cramp
What are the 4 states a womans uterus goes throu while preggers
1.Quiescence=In pregnancy, uterus inactive
2.Activation=Prepping for labour, uterus becomes capable of being activated
3.Stimulation=Labour itself w stimulation of uterine activity
4.Involution=PP return to pre-pregnancy state
Quiescence
What is it?
How is it maintained? (hormones)
-Represents time in utero b4 labour begins
-Relaxant prostaglandins, HCG, progesterone, CRH, protacylin, relaxin, nitric oxide, parathyroid related peptide + maybe more supress uterine activity=maintain quiescence
CRH=corticotrophin-releasing hormone
How does progesterone maintain Quiescence?
-Supresses prostaglandin production
-Blocks formation of oxytocin receptors +gap-junctions (which initiate contractions etc)
-Inhibits communication btween myometrial cells
-Prevents ocytocin release
-Inhibits cervical softening
Whats activiation phase?
-Begins 4-6 wks bfore labour
-Ends at physiological onset of labour
-Rising lvls of activating hormone oestrogen
-Has opposite effects of progesterone
How does oestrogen affect activitation phase?
-Promotes formation of oxytocin receptors + gap junctions in myometrium
-This effectively ‘wires up’ the uterus for contractions in labour
-Which further enables uterus to respond to existing concentrations of oxytocin since sensitivity is dependant on receptor density rathwe than increased output of oxytocin.
-Promoting cervical ripeninh
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