Preterm birth Flashcards
What are the classifications of prematurity
Below 37 weeks Late 34-36 Moderate 32-33 Very 28-31 Extreme <28
What are the classifications of low birth weight
LBW <2500g
Very <1500g
Extreme <1000g
What are the complications of prematurity
Sepsis, respiratory, cardiovascular, gastrointestinal, metabolic, sensory, cerebral palsy, neurodevelopmental delay, ADHD, insulin resistance, hypertension
Infant mortality improved, long term health not
What causes preterm parturition syndrome
Uterine overdistension Decidual haemorrhage Cervical insufficiency Infection + inflammation Other known/unknown causes
Describe the link between infection and preterm labour
Strong evidence for causal relationship
Emptying of infected cavity to protect mother and preserve reproductive function
Describe how the uterus can become infected
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
What is the mechanism by which infection causes preterm birth
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
What are the defences against infection in the reproductive tract
Acidic vaginal pH
Cervical mucus
Epithelial barriers
Innate immune system receptors (TLRs)
What is the relationship between ischaemia and preterm birth
Observational evidence links placental vascular lesions with preterm birth
Mechanism unclear
Severe ischaemia may act via thrombin
How does thrombin activate the pathway of labour
Stimulates myometrial contractility in dose dependent manner
Stimulates MMP production, degrades collagen in membrane and cervix
How does cervical insufficiency cause preterm labour
Premature cervical ripening
More likely in patients with anatomically disrupted cervic
How does uterine overdistension cause preterm labour
Term equivalent levels of stretch reached earlier in pregnancy
Increased expression of gap junction proteins + oxytocin receptor
Higher levels of collagenase + IL8 in membranes
How do endocrine disorders cause preterm labour
Progesterone promotes uterine quiescence, inhibits cervical ripening
Inflammatory pathways may contribute to progesterone withdrawal
How is preterm birth predicted
History based risk assessment Ultrasound cervical length screening Predictive tests- fetal fibronectin Infection screening Clinical diagnosis
What are the future possibilities for predicting preterm birth
Serum biomarkers
Impedance spectrosopy
Other cervical techniques
What are the risk factors for preterm birth
Previous preterm birth, multiple pregnancies, previous cervical surgery, uterine anomalies, smoking, race, age, bacterial vaginosis, short cervix
What is fetal fibronectin
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
What are the categories of preterm birth prevention
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
How does progesterone prevent preterm birth
Thought to affect myometrial contractility + cervical remodelling but possib;y via antimicrobial mechanisms
How does cervical cerclage prevent preterm birth
Placemetn of suture to prevent dilation of cervix
Conflicting evidence base due to trial hetergeneity
What are the different classifications of cervical cerclage
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
How is cerclage done
Mcdonald suture
Purse string non absorbable suture inserted around cervix
Left in place until late in 3rd trimester
What is the evidence for cervical pessary in preventing preterm birth
Flexible silicon ring supports cervix
1 RCT showed effective
More studies needed
What is the role of antibiotics in preterm labour
Only given in UK if there is preterm birth with broken waters
Can treat asymptomatic bacteriuria, bacterial vaginosis, periodontal disease, group B strep
What were the results of the ORACLE studies
1- antibiotics reduced neonatal morbidity + mortality, prolonged pregnancy by 7 days
2- No benefit or harm but reduced maternal deaths, cerebral palsy rate increased
How is preterm delivery prepared for
Antenatal corticosteroids
In utero transfer to appropriate unit
MgSO4
Tocolysis
What is the role of antenatal corticosteroids
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
What is the role of MgSO4 in preterm delivery
Reduces incidence of cerebral palsy
What is the role of tocolytics in preterm delivery
Can delay delivery by 1 week
Nifedipine- calcium channel blocker
Atosiban- oxytocin receptor agonist
