Pre-term birth Flashcards
Define premature infant
Born before 37 weeks
they can be small or adequate for their gestational age
Define low birthweight infant
<2500g at birth regardless of gestational age (5.5 pounds)
They could be appropriate for gestational age in which case they are premature
Or could be small for gestational age and either premature or term
What are the long-term sequelae of prematurity?
developmental delay
visual impairment
chronic lung disease
cerebral palsy
What advancements have meant that premature babies are able to survive?
Antibiotics Antenatal steroids Artificial surfactant Ventilation Nutrition
What are the causes of preterm delivery?
Spontaneous
- pre-term labour
- premature preterm rupture of membranes
- cervical weakness
- amnionitis
Iatrogenic - medically indicated
What is the trend in the percentage of babies born prematurely or LBW over time?
Has increased since 1990
What are the risk factors for pre-term birth (ie spontaneous pre-term labour)?
Race
Previous pre-term birth
Genital infection eg bacterial vaginosis
General infection - UTI, pylonephritis, appendicitis
Cervical weakness
Antepartum haemorrhage and other vaginal bleeding
Multiple pregnancy
Socioeconomic status
Smoking
IVF
Describe the pathophysiology of choriodecidual bacterial infection and preterm birth
There is both a maternal and foetal response to the infection
- The fetus has increased cortisol production and the mother has increased cytokines and chemokine production
- Both of these result in increased prostaglandins
- Increased myometrial contractions
- Increased metalloprotease production
- Cervical ripening, choriamnion weakening and rupture
- preterm delivery
So in a nutshell:
- fetal and maternal response to infection
- increased prostaglandins
- uterine contractions
- metalloproteases weaken the chorioamnion and cause cervical ripening
What are the three categories of prevention of pre-term birth?
Primary
Secondary
Tertiary
What are the approaches to primary prevention of pre-term birth?
(not demonstrated to be effective yet) Smoking cessation STD prevention Prevention of multiple pregnancy Variable work schedules Planned pregnancy Physical and sexual activity advice Cervical assessment at 20-26 weeks
What does secondary prevention mean in terms of pre-term birth?
Identifying those pts at increased risk of PTB and providing prophylaxis and suveillance
Which women are screened for PTB?
High risk:
- 2nd trimester miscarriage
- previous early 3rd trimester delivery (before 32 weeks)
- PPROM (before 32 weeks)
How are high risk women screened and managed for PTB as part of secondary prevention?
- High vaginal swab at booking (11 weeks) for bacterial vaginosis - treat with single dose 2g metronidazole
- Transvaginal cervical ultrasound at 14 weeks, then repeat every 2 weeks till 28 weeks
- Qualitative Fetal fibronectin test
- progesterone - IM injection or pessary
What does a transvaginal ultrasound screen for?
Opening of the internal os and resulting reduced length of the cervical canal
How long is a cervix that is classified as a threatened preterm labour cervix?
<3cm
normal is at least 3 cm
What is measured in the screening transvaginal ultrasound?
Cervical length - distance between internal and external os
Look for funnelling - ie open internal cerivcal os, if present, measure the funnel length
What is fetal fibronectin (fFN)?
Extracellular matrix protein found in choriodecidual interface
What is the significance of fetal fibronectin (fFN)?
It is a signal that the baby is coming…
Abnormal finding after 20 weeks
As it indicates disruption of attachment of membranes to decidua
its normal for it to be present before labour - as the baby is coming
How do you test for fFN?
high vaginal swab of the posterior fornix
What are the reasons for a false positive fFN?
Cervical manipulation ie vaginal examination
Sexual intercourse
Lubricants
Bleeding
What is the principle of tertiary prevention of pre-term labour?
Treatment after diagnosis of pre-term birth
What are the clinical signs of pre-term labour?
Persistent contractions - painless or painful
Intermittent abdo cramping, pelvic pressure or back pain
Increased or change in vaginal discharge
Vaginal spotting or bleeding
What are the approaches to tertiary prevention of pre-term birth?
- Prompt diagnosis and referral
- Antibiotics
- Tocolytic (Atosiban: an oxytocin receptor blocker) - tocolytics suppress uterine contractions
- Steroids - for maturation of babies lungs
What is the definition of preterm labour?
Persistent uterine activity AND change in cervical dilatation and/or effacement
How would you examine a pt presenting with possible pre-term labour?
- sitting pulse and BP - maternal infection
- temp - for chorioamnionitis (is a contraindication of suppression of pre-term labour)
What investigations would you do for a pt presenting with possible pre-term labour?
- FBC - CRP and WBC - for chronioamniotis
- CTG
- Sterile speculum examination
- vaginal pH - bacterial vaginosis
- High vaginal swab - bacterial vaginosis, fetal fibronectin
- Endocervical swabs - chlamydia and gonorrhoea
- Low or high vaginal swab - group B strep - Transabdominal USS
- plancental location
- amniotic fluid volume - has she leaked liqour
estimated fetal weight and presentation - in case she goes into labour
- fetal well being - is the baby alive or not - Transvaginal USS
- cervical length <3cm and contractions = pre-term labour - cervical examination
- assess dilatation and effacement
When do you test for group B strep in pregnancy?
- ruptured membranes
- pre-term labour
- vaginal discharge
Why is it important to treat group B strep in pregnancy?
- can cause chroiamnitis and neonatal sepsis, pneumonia and meningitis and neonatal death particularly in pre-term babies or in distressed babies (eg placental insufficiency)
- can cause pre-term labour if there are ruptured membranes
