Preterm labour (PTL) is the onset of labour (regular uterine contractions and cervical effacement and dilatation) between the limit of viability and term. In practice, it is defined as labour between 20 and 37 completed weeks of gestation.
The history is notoriously unreliable in the diagnosis of PTL, as the only symptom (maternal perception of contraction frequency or strength) is a poor guide to the outcome. Approximately 50% of patients presenting with threatened PTL will deliver at term even without treatment (Lockwood et al. 1991). However, in a proportion of patients, temporal changes in symptoms within an individual are helpful in guiding management. Clinical examination, particularly palpation of the uterus is often unreliable in assessing contraction strength. Vaginal speculum examination is useful however, to determine cervical effacement, dilation and the presence of amniotic fluid. Digital vaginal examination should be avoided if the membranes are ruptured to reduce the risk of introducing infection.
Further history and examination should include determination of the gestational age and presenting part, and elicit symptoms or signs of chorioamnionitis, maternal medical conditions (diabetes, thyrotoxicosis, cardiac disease, hypertension), pregnancy specific disorders (pre-eclampsia) and possible precipitating conditions in the current pregnancy (abruption, placenta praevia, multiple pregnancy, ruptured membranes). Fetal condition and presentation should also be assessed (Table 8.1).
Specific investigations will be directed by clinical symptoms and signs although urinalysis (to exclude infection) and a full blood count are indicated in the majority of women.