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Flashcards in Normal birth Deck (15):

What are the three areas of labour

Passenger, passage and power.


What are the phases of human parturition?

Quiescence - of uterus with growth. Uterine muscle contractions poorly synchronised (Braxton-Hicks). Painless because low amplitude and frequency. Cervix is firm and closed.
Progesterone maintains quiescence

Timing- for safe birth. We don't know what impacts timing. Heavy stress may induce a stress response, such as IL-6, TNF-alpha and CRP that can induce early labour.

Activation - Requires an intact fetus, stretching of the uterus induces labour, and rupturing of the membranes induces labour. Premature labour can be caused by membrane rupture.
Three things happen in activation:
Activation of the myometrial musculature
Cervical changes (ripening, softening, shortening, effacement). Membrane rupture. The main simulator is prostaglandins

Birth - pelvic ligaments soften to allow extra 1 cm of pelvic diameter, cervix soft and easily dilated, membrane rupture (damage causes more prostaglandins), fetal-neonatal adaptations (breathing, cardiovascular changes)

Involution - (mother) - occurs after placental separation, cleavage through decidua basalis, haemostasis, contractions to prevent postpartum haemorrhage, increased uterine sensitivity to oxytocin to cause uterus to contract (half weight within a week), establishing lactation.


What hormone maintains quiescence and how is it involved in the induction of labour?

Progesterone, which comes from the corpus leuteum/placenta

Withdrawal of progesterone causes labour. In humans, this is done by reducing the two progesterone receptors and not changind the blood progesterone levels. Mifepristone blocks both receptors to initiate labour.

Progesterone reduces prostaglandin F which produces oxytocin and induces uterine contraction. It also effects Ca2+ transport, and increases beta adrenergic receptors.

Decreased Ca2+ also maintains quiescence.
Also NO


What drug can be used to initiate labour and what does it do?

Mifepristone blocks both progesterone receptors to initiate labour.

Progesterone reduces prostaglandin F which produces oxytocin and induces uterine contraction. It also effects Ca2+ transport, and increases beta adrenergic receptors.


What happens when labour is induced (activation?)

Increase in gap junctions between the myometrial cells.
Prostaglandin (not progesterone) and oxytocin recptors are upregulated on myometrial cells and these wire the different muscle cells together, coordinating the contractions.

Increase contractility (block with Ca channel blockers e.g. nifedipine),
Increase myocyte excitability
Increase intracellular connectivity gap jucntions (antagonise with PG synthase inhibitors (COX1 and COX2)


What induces labour?

Placental clock - requires intact fetus.
Progesterone withdrawal, placenta estrogins

Prostaglandins. - Increase the contractility of myometrium and induces membrane rupture. Cause changes to the cervix.


What is the role of oxytocin?

It induces contractions of the uterus during birthing and after labour to stop bleeding. Can also be used to induce labour but is not potent at this role, only when everything is nearly ready.


What remodels the cervix?

Cytokines, IL-8, TNF-alpha, IL-1beta. These cause breakdown of the extracellular matrix and softening of the cervix. This is an inflammatory response that can also be induced by infection.


What are the stages of labour?

1) until full dilation (10 cms) - Contractions, cervix effacement and dilation, babys head coming into the pelvis. Membranes rupture.

2) full dilation until birth of baby.
3) Birth of baby until delivery of the placenta.


At what stage is there no stopping labour?

When women are in the active phase - contractions, pain and 5 cm of dilation.


What are the adaptions that occur after birth?

Establishment of breathing.

Cardiovascular: Closure of the foramen ovale.
Reduced pulmonary vascular resistance.
Closure of the ductus arteriosus.

Thermogenesis: non-shivering, brown fat. Dry the baby to prevent heat loss.

Suckle: establish suckeling, also causes the uterus to contract.


What can be used to prevent labour?

See next lecture: Tocolysis


What can be used to induce labour?

Prostaglandins (pill), mifepristone


What can promote involution?

Oxytocin, prostaglandins, tranexamic acids.


What is the role of prostaglandins in labour?

Increase myometrial contractility
Cause contractions
Leads to cervix changes
associated with membrane rupture.