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Fetus > Preterm birth > Flashcards

Preterm birth Flashcards

1
Q

What are the classifications of prematurity

A 
Below 37 weeks
Late 34-36
Moderate 32-33
Very 28-31
Extreme <28
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2
Q

What are the classifications of low birth weight

A

LBW <2500g
Very <1500g
Extreme <1000g

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3
Q

What are the complications of prematurity

A

Sepsis, respiratory, cardiovascular, gastrointestinal, metabolic, sensory, cerebral palsy, neurodevelopmental delay, ADHD, insulin resistance, hypertension
Infant mortality improved, long term health not

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4
Q

What causes preterm parturition syndrome

A 
Uterine overdistension
Decidual haemorrhage
Cervical insufficiency
Infection + inflammation
Other known/unknown causes
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5
Q

Describe the link between infection and preterm labour

A

Strong evidence for causal relationship

Emptying of infected cavity to protect mother and preserve reproductive function

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6
Q

Describe how the uterus can become infected

A

Ascending- most common route
Microorganisms reach decidua, stimulate local inflammatory reaction
Production of proinflammatory cytokines + inflammatory mediators
Then microorgansims can cross into cavity, stimulate production of inflammatory mediators by resident macrophages
Microorganisms that reach fetus can elicit systemic inflammatory response syndrome
Also: haematogenous via placenta, retrograde seeding, iatrogenic

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7
Q

What is the mechanism by which infection causes preterm birth

A 
IL-1 is produced by decidua in response to bacterial products, stimulates PG production + myometrial contractions
Also TNFa, IL10
Increased cytokines + chemokines
Neutrophil infiltration
MMPs
Adrenal cortisol
CRH
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8
Q

What are the defences against infection in the reproductive tract

A

Acidic vaginal pH
Cervical mucus
Epithelial barriers
Innate immune system receptors (TLRs)

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9
Q

What is the relationship between ischaemia and preterm birth

A

Observational evidence links placental vascular lesions with preterm birth
Mechanism unclear
Severe ischaemia may act via thrombin

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10
Q

How does thrombin activate the pathway of labour

A

Stimulates myometrial contractility in dose dependent manner

Stimulates MMP production, degrades collagen in membrane and cervix

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11
Q

How does cervical insufficiency cause preterm labour

A

Premature cervical ripening

More likely in patients with anatomically disrupted cervic

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12
Q

How does uterine overdistension cause preterm labour

A

Term equivalent levels of stretch reached earlier in pregnancy
Increased expression of gap junction proteins + oxytocin receptor
Higher levels of collagenase + IL8 in membranes

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13
Q

How do endocrine disorders cause preterm labour

A

Progesterone promotes uterine quiescence, inhibits cervical ripening
Inflammatory pathways may contribute to progesterone withdrawal

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14
Q

How is preterm birth predicted

A 
History based risk assessment
Ultrasound cervical length screening
Predictive tests- fetal fibronectin
Infection screening
Clinical diagnosis
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15
Q

What are the future possibilities for predicting preterm birth

A

Serum biomarkers
Impedance spectrosopy
Other cervical techniques

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16
Q

What are the risk factors for preterm birth

A

Previous preterm birth, multiple pregnancies, previous cervical surgery, uterine anomalies, smoking, race, age, bacterial vaginosis, short cervix

17
Q

What is fetal fibronectin

A

Extracellular matrix protein in chriodecidual interface
Abnormal to find in cervicovaginal fluid after 20 weeks
Reappears close to labour
10 min test with ELISA with FDC6 monoclonal antibody
Qualitative and quantitative results
Cervical manipulation, sexual intercourse, lubricants, bleeding can cause false positives
High negative predictive value, low positive predictive value

18
Q

What are the categories of preterm birth prevention

A

Primary- aim to reduce population risk, effective interventions not yet demonstrated, smoking reduction etc
Secondary- targeted at those with increased risk- cervical length screening, cerclage, progesterone
Tertiary- treatment after diagnosis, aim to reduce morbidity + mortality. Tocolysis, antenatal corticosteroids

19
Q

How does progesterone prevent preterm birth

A

Thought to affect myometrial contractility + cervical remodelling but possib;y via antimicrobial mechanisms

20
Q

How does cervical cerclage prevent preterm birth

A

Placemetn of suture to prevent dilation of cervix

Conflicting evidence base due to trial hetergeneity

21
Q

What are the different classifications of cervical cerclage

A

History-indicated cerclage- risk factor based, usually 12-14 weeks
Ultrasound indicated- in response to cervical length shortening but no exposed fetal membranes
Rescue cerclage- therapeutic salvage after cervical dilation with exposure of fetal membranes

22
Q

How is cerclage done

A

Mcdonald suture
Purse string non absorbable suture inserted around cervix
Left in place until late in 3rd trimester

23
Q

What is the evidence for cervical pessary in preventing preterm birth

A

Flexible silicon ring supports cervix
1 RCT showed effective
More studies needed

24
Q

What is the role of antibiotics in preterm labour

A

Only given in UK if there is preterm birth with broken waters
Can treat asymptomatic bacteriuria, bacterial vaginosis, periodontal disease, group B strep

25
Q

What were the results of the ORACLE studies

A

1- antibiotics reduced neonatal morbidity + mortality, prolonged pregnancy by 7 days
2- No benefit or harm but reduced maternal deaths, cerebral palsy rate increased

26
Q

How is preterm delivery prepared for

A

Antenatal corticosteroids
In utero transfer to appropriate unit
MgSO4
Tocolysis

27
Q

What is the role of antenatal corticosteroids

A

Significantly reduces neonatal death
Accelerates production of type 1 + 2 pneumocytes in lung
Increases sodium channels in alveoli
Increased fluid reabsorption from fetal lung
Increases surfactant production

28
Q

What is the role of MgSO4 in preterm delivery

A

Reduces incidence of cerebral palsy

29
Q

What is the role of tocolytics in preterm delivery

A

Can delay delivery by 1 week
Nifedipine- calcium channel blocker
Atosiban- oxytocin receptor agonist

Fetus (18 decks)

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