Rate of sonographic cervical shortening and the risk of spontaneous preterm birth.

OBJECTIVE

We hypothesized that change in cervical length (CL) on serial ultrasounds is associated with spontaneous preterm birth (SPTB) <36 weeks for women with a short cervix (CL <25 mm).

STUDY

DESIGN

This was a secondary analysis of a multicenter prospective observational study designed to study predictors of preterm birth. Women from the general obstetric population had serial CL ultrasounds between 20-33 weeks' gestation and were followed up until delivery.

RESULTS

Two thousand six hundred ninety five women had sonographic CL measurements. Change in CL was associated with SPTB for women with CL <25 mm (odds ratio, 0.97; 95% confidence interval, 0.96-0.98). Among women with a short cervix, for every 1 mm of cervical shortening between ultrasounds, there was a 3% increase in odds of SPTB. The association between change in CL and SPTB remained significant after controlling for age, race, body mass index, tobacco use, and fetal fibronectin test status.

CONCLUSION

Among women with a sonographically short cervix, the rate of change in CL is associated with SPTB, independent of fetal fibronectin test and other important risk factors for SPTB.