Factors associated with preterm labour and changes in the cervix before labour in twin pregnancy.

A total of 132 twin pregnancies in black African women were studied prospectively after 30 weeks gestation. Delivery occurred before 37 weeks in 32%. There was a trend (0.1 greater than P greater than 0.05) towards a higher preterm delivery rate in nullipara (57%), in women under the age of 20 years (60%) and in those with a height/weight ratio of greater than 2.5 (50%). The cervix was assessed with a score based on the length of the canal minus the dilatation of the internal os. In both term and preterm labour there was a significant relation between a cervical score of 0 or a decrease in cervical score and the onset of labour within the subsequent 14 days (P less than 0.001). By these criteria to predict impending labour, 60% of all labours that ensured within 14 days of the assessment would have been predicted with a 20% false positive rate. When nulliparae were excluded the predictive value of cervical assessment for preterm labour was 80% with a false positive rate of less than 5%. Plasma oestriol levels were significantly higher in the preterm labour group but had no clinical prognostic value.