Page created on January 4, 2022. Last updated on April 2, 2022 at 15:00
Definition and epidemiology
Threatened preterm delivery is a vague term used to define a situation where preterm delivery may be imminent, requiring the need for management to try to postpone delivery as long as possible. The most common finding which raises alarms for threatened preterm delivery is regular contractions ahead of week 37.
Past gestational week 34, there is no need to attempt to delay premature labour, as the perinatal outcome is so good at that point that applying the measures used to delay labour are no longer justified.
Only a minority of women who present with threatened preterm delivery progress to actual labour and delivery. However, if preterm prelabour rupture of membranes (PPROM) (topic A6) occurs, labour is inevitable.
- History of preterm birth
- Cervical insufficiency
- Multiple gestation
- Genital infection
The following may be signs of threatened preterm labour:
- Regular, painful uterine contractions less than 10 minutes apart lasting more than 1 hour (most common)
- Other symptoms of labour (lower back pain, blood-tinged vaginal mucus)
- Cervical dilation or effacement
Diagnosis and evaluation
If there are signs of a possible threatened preterm delivery, we must determine whether this is a false alarm or whether preterm delivery truly is inevitable. The following findings suggest preterm labour is likely (their absence suggest it’s unlikely):
- Cervix dilated > 3 cm (and cervical dilation increases over time)
- Cervical length < 20 mm
- Foetal fibronectin level is positive
Foetal fibronectin is a protein which is released into cervicovaginal secretions in case of true preterm labour. It may be measured to distinguish women in true preterm labour from those in false labour.
In case preterm delivery may be imminent, glucocorticoids (betamethasone or dexamethasone) are administered IM to the mother in two doses, the second dose repeated 24 hours after the first. Glucocorticoids hasten maturation of the foetal lungs (by stimulating surfactant production), reducing the incidence of neonatal respiratory distress syndrome (NRDS) as well as perinatal morbidity and mortality in general. This effect occurs as early as a few hours after the first dose, but the maximum effect is not achieved until 24 hours after the second dose. The effect lasts approximately 7 days.
Tocolytics (beta mimetics, atosiban, nifedipine) may be used to delay labour for a few days, allowing the glucocorticoids to take effect.
Magnesium sulphate administration is neuroprotective and reduces the risk of cerebral paresis in case of preterm birth. It’s recommended in case of threatening preterm labour.
Antibiotics (penicillin, ampicillin) may be administered to reduce the risk for GBS infection.
Possible complications of preterm birth include:
- Neonatal respiratory distress syndrome (NRDS)
- Bronchopulmonary dysplasia
- Necrotising enterocolitis
- Retinopathy of prematurity
- Periventricular leukomalacia