Preterm labour

Question 1

What is preterm labour?

Answer 1

Less than 37 weeks, very preterm is before 32 weeks.

Excellent survival from 28-29 weeks but not perfect health.

It is more than a date, it is a failure of uterine quiescence.

Question 2

What are disorders associated with being born early?

Answer 2

Periventricular leukomalacia (brain bleed),
Retinopathy of prematurity
Chronic lung disease - not enough surfactant - main problem
Necrotising entercolitis
Pneumothorax
Neurodevelopmental

Cerebral palsy
Sight and hearing issues
Respiratory problems
Low IQ,
Behavioural problems, social, economic, family-personal

Question 3

What are some causes of spontaneous preterm birth?

Answer 3

Failure of quiescence.

Intrauterine stretch - increasing prostaglandins and leading to cervical ripening and uterine activation. It also increases cytokines leading to membrane rupture.

Intrauterine haemorrhage - increased prostagandins leading to cervical ripeningand uterine activation. It also causes membrane rupture.

Intrauterine infection - increased cytokines and chemokines leading to membrane rupture, it also increases prostaglandins resulting in cervical ripening and uterine activation.

Inflammation reduces progesterone receptors.

Stressed fetus, upreguation of the myometrium or cervical problems will cause early labour.

Spontaneous:Infection, multiples, fetal abnormality, uterine or cervical abnormality,
Iatrogenic: maternal disease, fetal health.

Question 4

What happens during cervical ripening?

Answer 4

Inflammation process
Infiltration of leukocytes, increase in cytokines, increase in metalloproteases,

This cervix function is independent of uterine activity.

Question 5

What causes loss of quiscence?

Answer 5

Disruption of progesterone and its receptor.

Infection (main)
Stretch - membrane disruption, myometrial distension
Tissue damage especially the cervix
Placenta -growth of fetus poor (poor attachment or growth problems)
Congenital abnormalities of the cervix
Some cercadian association - always early morning.

Infection, multiples, fetal abnormality, uterine or cervical abnormality, maternal disease, fetal health.

Question 6

What are the layers of the sac and uterus and where can infections occur?

Answer 6

Amnion, chorion, decidua, myometrium.

Can get an infection from the blood to the fetus or from the vagina, through the cervix, in the choriodecidual space to the placenta and then the the fetus.

Question 7

What do prostaglandins do in labour?

Answer 7

It is created from arachadonic acid from the cell membranes and cause:
Myometrial contractility
Cervix changes
Membrane rupture

Question 8

What are problems of preterm birth?

Answer 8

Immature fetus - often unwell
Often malpresentation - breech
Often have complicated cesarean sections
Often have maternal comorbidities
Risk of recurrence
May have poor outcomes

Question 9

What situations required iatrogenic preterm birth?

Answer 9

Maternal disease (preeclampsia)
Fetal health - fetal growth restriction.

Question 10

What is placenta vascular disease?

Answer 10

Vascular damage to the placenta, infarcts and haemorrhage in placenta.
Can result in preterm and growth restricted baby.

Question 11

What are the risk factors for preterm delivery?

Answer 11

Non-modifiable risk: maternal age, obstetric history (previous preterm baby), scioeconomic status, race. Short cervical length.

Modifiable risk: smoking, no prenatal care, need for cervical surgery (can wait?), reproductive technologies (prevent multiple pregnancies)

Others: uterine anomaly, maternal disease, antepartum bleeding, polyhydramnios

Question 12

How can the cervix be used to predict preterm birth?

Answer 12

Short cervix is associated with preterm birth.

Question 13

What is another way to screen for preterm birth risk?

Answer 13

Cervico-vaginal fluid levels of fetal fibronectin.

Fibronectin sits between the chorion and the decidua (glue). Undetectable in normal pregnancy up until week 36 weeks. High in early pregnancy and later pregnancy as the sac is formed and moved in preperation for labour.

Positive test - 30% deliver in 7-10 days.
negative test - 99.5% don’t deliver in 7-10 days.
Can use to decide who to transfer and who to treat with steroids.

Question 14

How do you suppress preterm labour?

Answer 14

Tocolysis (medications to suppress labour)
Ca2+ channel blockers (nifedipine) - prevents myometrium contraction.
Oxytocin receptor blocker (atosiban)

Question 15

What does nifedipine do?

Answer 15

Ca2+ channel blocker to suppress labour. Only works acutely, can’t be given for maintenance.

Question 16

What does atosiban do?

Answer 16

Oxytocin blocker to suppress labour

Question 17

What drugs can be given antenatally to reduce mobidity?

Answer 17

Corticosteroids given to the mother- dexamethasone - prevention of neonatal death from respiratory distress, and reduces intraventricular haemorrhage (premature bleeding), reduces rates of necrotising entercollitis (infection in the gut wall of the baby).

If the baby is under 30 weeks gestation give the mother i.v. magnesium sulphate - reduces the risk of cerebral palsy

Question 18

What can be done to prevent preterms happenig again?

Answer 18

Remove recurrent cause if possible:
Smoking (if you could stop women smoking in pregnancy you would reduce preterm births by 50%)
Cervical cerclage - nylon stitch in cervix

Drug therapies - progesterone as a vaginal cream can reduce spontaneous PTB by 45%. Progesterone therapy effective for those with a short cervix <25 mm and greater than 10 mm. Good for single pregnancies only. Not effective i.v. and not effective once contractions have started.

Preterm birth clinics

Question 19

If a pregnant woman comes into the clinic what should be done?

Answer 19

Perform a risk assessment (social, smoking, prior preterm birth), assess maternal health
If high risk: Measure the length of the cervix with ultrasound
Perhaps give progesterone and/or cervix cerclage.
If she comes in and is threatening preterm labor then check for fetal fibronectan levels toconfirm and if positive give dextamethasone and magnesium sulphate.

Aspirin and calcium can be used to reduce growth restriction and prevent preeclampsia, respectively.

Question 20

What does mifepristone do?

Answer 20

Antagonises progesterone receptors and facilitates labor