Normal birth Flashcards by Emily Stephens

The three P’s of birth

Passage, Passenger, Powers

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Physiological processes of parturition

Quiescence - of uterus with growth, distension, pressure
Timing- for safe birth
Activation- stimulation of uterine musculature changes in genital tract
Birth- fetal-neonatal adaptations
Involution- haemostasis, establishing lactation

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What is labour?

Getting the fetus from the uterus to the outside world

• ie, uterine activity and cervical change which leads to the expulsion of the fetus and placenta

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Anatomical changes leading to birth

UTERUS
UPPER AND LOWER SEGMENTS

CERVICAL CHANGES - RIPENING

SOFTENING SHORTENING EFFACEMENT

MEMBRANE RUPTURE

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Quiescence

For most of gestation the uterus remains ‘quiet’
There are small and painless uncoordinated contractions.
Cervix remains firm and closed

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Quiescence and hormones? Where do they come from?

Progesterone is the main hormone responsible for uterine quiescence. Comes from placenta and corpus luteum.

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Progesterone changes with birth?

In humans progesterone doesn’t decrease at the time of birth. Receptor expression changes. Relative balance between PR- A and PR-B is important.
Mifepristone is an antiprogesterone and it blocks A and B induces labour - and abortion.

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Progesterone and PGs

Progesterone reduces the synthesis of Prostaglandin F, PGF is responsible for oxytocin which makes the uterus contract. It also effects calcium transport and also increases beta adrenergic receptors.

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Gestation length is determined by?

Parity
Age
Genetics- maternal and paternal
Race- Ethnicity

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Stress and Labour

Mediated through cytokines or acute phase reactants.
There is evidence that is you are in a very stressful environment - manual labour - disturbed circaidian patterens - maybe some of APRs are elevated and shorten gestation. Has to be severe.

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Activation

Timing – uncertain process in Humans 280days from LMP (37-42wks)
• Activation involves fetal genome
uterine stretch- growth
fetal HPA axis
upregulation of myometrium
Melatonin and circadian rhythms
abnormally if membranes rupture prelabour

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Activation- upregulation of myometrium

Before you go into labor you get an increase in PG receptors, Oxytocin receptors and gap junctions linking everything together.

Labor - lots more wiring uterus is activated and ready to go.

Instead of uncoordinated BH contractions you get coordinated strong contractions.

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Contraction associated proteins

Increased myometrial activity - actin and myosin

Increased myocyte excitability ion channels - Ca2+

↑intercellular connectivity gap junctions

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Main modulator of activation

Withdrawal of Progesterone from the PG receptors modulates this cascade, the uterus get itself ready to be stimulated and the main stimulators are PGs.

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PGs and Labour

The final establishment of labor is an inflammatory event through PGs.

PGs are the most potent inducers of labor.

PGE predominant

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PGs effect in labour

Increase myometrial contractility

Lead to cervix changes

Associated with membrane rupture

Oxytocin- when do we use it?

Use it to stimulate labor and after labor to induce uterine contraction and stop the woman bleeding.
Not good at starting labor.
Nonapeptide from the posterior pituitary and genital tract

The Cervix - cervical ripening

Closed cervix prevents ascending infections from vagina. Has to soften and open up to deliver baby.

1. Firm cervix
2. Gets remodelled by a whole lot of cytokines
3. ECM breaks down.

Can happen at term cos estrogen rises and progesterone falls.
Can happen preterm cos of inflammatory process.

Fetal membranes

Amnion and chorion
• Site of PG production
• Rupture not essential for labour
• Rupture at Zone of altered morphology
• Amniotomy in normal labour small effects on progress
• A method of inducing labour

The Zone of altered morphology

At lower segment of uterus - we have the zone of altered morphology - more receptors in that area that you can get more PG synthesis.

Ideal birth setup

Mature fetus - timing right
Pelvic ligaments - softened
extra 1+ cm pelvic diameters
Uterus excitable and contractions coordinated
Cervix soft and easily dilated
Membranes may rupture –more PGs and possible mechanical benefits

The stages of Labour

1 - until full dilatation 10cm
2- full dilatation to birth of the baby
3- from birth to placental birth

What is a Partogram?

the graphic description of labour

What happens during the first stage of labour?

Contractions
Cervical effacement & dilatation
Descent of the presenting part
SRM - spontaneous rupture of membranes
ROM - rupture of membranes – PROM - premature ROM

What is the first thing a baby has to establish at birth?

First thing baby has to establish breathing. 90% transition easily from fetus to neonate. 10% need some help to breathe. 1% need major resuscitation

Cardiovascular adaptations in the neonate

Closure of foramen ovale 100% Rt vent output through lungs Reduction Pul vasc resistance Reduction-closure ductus aretiosus

What need to happen to neonate pulmonary resistance?

Has to be a rapid reduction in the pulmonary vascular resistance to allow blood to traverse the lungs and be oxygenated.

Thermogenesis

Baby needs to maintain heat - dry baby to avoid evaporative heat loss. Stimulation also help baby breath. Non shivering-vascular brown fat Sympathetic nervous control Term neonates can maintain body temp to ambient 230 C (30-60mins)

Birth and feeding

Fetus- constant supply of nutrients Neonate-intermittent feeding risk of hypoglycaemia Establishment of Lactation- breast feeding

Clinical outcomes in Labour

Around 6 women per 10'000 go into labor with a live baby but then birth a not alive baby. Also a number of babies which suffer from neonatal encepholopathy - long term handicap. (Excludes the 15% of women that get pregnant and miscarry before 20 weeks).

Head Cooling

Early on in neonatal asphyxia you can cool the brain which can substantially reduce the damage done.

Involution

* Placental separation (begins after) * Cleavage through decidua basalis * Contractions to prevent postpartum haemorrhage * Increased uterine sensitivity to oxytocin

Suppressors of Labour?

Tocolysis | Progesterone

Activators of Labour?

Mifepristone, PGs, possibly | NO donors

Stimulators of Labour?

PGs, oxytocin

Stimulators of Involution?

Oxytocin, PG analogues, Tranexamic acid (PPH)

Summary | Normal labour-mechanisms?

Pregnancy hormones put the brake on myometrium Placental clock in humans (needs intact fetus) Placental oestrogens ↑ CRH Prog “withdrawal” (receptor level )↑ C43 Prostaglandins stimulate PrA Activation of circadian signalling

Summary of normal term labour?

An inflammatory process Multiple steps in a cascade complexity possibly protective Requires interplay between fetoplacental unit and myometrium Timing and initiation processes unknown in humans