Cervical length at 18-22 weeks of gestation for prediction of spontaneous preterm delivery in Hong Kong Chinese women.

OBJECTIVE

To assess the value of a single cervical length measurement by transvaginal sonography (TVS) at the time of mid-trimester anomaly scan for predicting spontaneous preterm delivery (SPD) among Chinese women.

METHODS

A prospective observational study was carried out involving 2880 subjects with singleton pregnancies and confirmed gestational age. Cervical length was measured at 18-22 weeks of gestation.

RESULTS

The incidence of SPD < 34 weeks and < 37 weeks were 0.7% and 3.7%, respectively. Women with SPD < 34 weeks and SPD < 37 weeks had shorter median cervical lengths (32.6 mm and 36.2 mm, respectively) than those with term deliveries (37.6 mm) (P = 0.006 and 0.025, respectively). The predictive performance of cervical length was better for SPD < 34 weeks compared with < 37 weeks. A cervical length < or = 27 mm, which corresponded to the 4th centile, occurred in 36.8%, 62.5% and 100% of those with SPD < 34, < 30 and < 26 weeks, respectively. The positive likelihood ratio (LR) of a cervical length < or = 27 mm in predicting SPD < 34 weeks was 9.8. Using logistic regression, both short cervix and funneling were independent predictors for SPD < 34 weeks of gestation. The coexistence of funneling and a cervical length < or = 27 mm gave a positive predictive value (PPV) and LR of SPD < 34 weeks of 14.7% and 26.0, respectively.

CONCLUSIONS

Mid-trimester cervical length is predictive of SPD in Chinese women. However, given the low PPV of a short cervical length, its clinical utility is still limited in low-risk populations.