Abstract
Methods: Retrospective cohort of 453 twin pregnancies in two tertiary centers over an 11-year period. All women had serial ultrasound assessment of CL from 11–13+6 weeks through to 14–15+6, 16–17+6, 18–19+6 and 20–21+6 weeks as part of routine antenatal care. A total of 720 serial CL measurements were recorded. Monochorionic twin pregnancies complicated with twin to twin transfusion syndrome and monoamniotic pregnancies were excluded. We estimated the association between cervical length at each of the five study periods and preterm delivery before 28, 32 and 34 weeks’ respectively. Results: The cumulative incidence of preterm delivery was 6.8%, 13.2% and 26.1% before 28, 32 and 34 weeks’ respectively. A CL below 50 mm at 11–13+6 weeks was associated with preterm delivery before 28 weeks (RR = 1.63, 95% CI = 1.21–2.18, P 45 mm for delivery before 28 (LR− 0.33) and 34 weeks (LR− 0.29) respectively. CL 50 mm at this gestation reflects a low likelihood of preterm delivery.
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