Tracking the trajectory of cervical length dynamics in uncomplicated dichorionic diamniotic twin pregnancies: A retrospective cohort study.

OBJECTIVE

We hypothesised that distinct patterns of serial cervical length change in dichorionic diamniotic twin pregnancies are associated with differential risks of preterm birth.

METHODS

A retrospective cohort study was conducted at the Twins Clinic of a tertiary fetal medicine unit. In total, 389 women with uncomplicated dichorionic diamniotic twin pregnancies underwent four weekly cervical length measurements. Changes in cervical length were classified into Pattern I (stable cervical length), Pattern II (early rapid shortening), Pattern III (late shortening) and Pattern IV (early shortening with a plateau). Association of each pattern with preterm delivery was assessed.

RESULTS

Pattern I was observed in 37.5% cases, Pattern II in 11.8%, Pattern III in 32.6% and Pattern IV in 18%. The proportion of patients delivering preterm was significantly higher in Pattern II (early rapid shortening), followed by Pattern III (late shortening). The mean period of gestation at delivery was 35.5 weeks in cases of Pattern I (stable cervical length), 30.7 weeks in Pattern II (early rapid shortening), 34.2 weeks in Pattern III (late shortening) and 34.9 weeks in Pattern IV (early shortening with a plateau). Patients in Pattern II (early rapid shortening) had a significantly shorter mean cervical length at both the nuchal scan and between 20-24 weeks, as well as a significantly greater decline in cervical length between these two time points, compared with those in Pattern IV (early shortening with a plateau).

CONCLUSION

Distinct patterns of cervical length shortening in uncomplicated dichorionic diamniotic twin pregnancies are linked to varying risks of preterm birth, thus making serial assessment more predictive than single measurements.