Description of Treatment/Procedure

Occurring in approximately 10% of all births in the United States, preterm deliveries (PTD) are a major problem in obstetrics. The incidence of birth before 37 weeks’ gestation has also been increasing over the years. Twin pregnancies are associated with a higher rate of morbidity and mortality than singleton pregnancies and preterm delivery is the major factor. About 5-10% of twin pregnancies deliver before 33 weeks’ gestation. Various measures have been used to determine who is at risk for PTD including clinical predictors (such as cervical length measurement), tests for genital tract inflammation and vaginal infection, and assessment of biochemical markers. For ultrasound cervical length to be a reliable tool in predicting preterm labor (PTL), the methods of cervical examination and measurement need to be standardized.

Committee Summary

With regard to the use of ultrasound cervical length for the prediction of preterm labor, the ICSI Technology Assessment Committee finds:

1. Cervical length is a biological continuum.
   
2. Ultrasound measurement of cervical length is not recommended as a screening test for preterm labor in the general obstetric population.
   
3. Ultrasound is a safe procedure. The risks and limitations of the test are related to the false negative rate and the false positive rate.
   
4. Many studies have shown an inverse relationship between cervical length and the risk of preterm delivery.
   
5. The clinical benefit of cervical length measurements may rest in the benefit of a negative (normal) result (i.e. >25 mm) which would prevent unnecessary interventions in women who have signs and/or symptoms of preterm labor. The clinical significance of a short cervical length (i.e. <25 mm) remains unclear. Negative predictive values have ranged from 77%-96% and positive predictive values have ranged from 27%-100% for a 25 mm cutoff between 18-28 weeks’ gestation (Conclusion Grade II).
   
6. High-risk patients with changes in their cervical length between 18-28 weeks’ gestation or with the appearance of a funnel or beak at the internal os that comprises about 40-50% or more of the total cervical length have been shown to be at increased risk of preterm delivery.
   
7. Although cervical length measurement between 28-35 weeks’ gestation may be clinically helpful, its usefulness has not been supported in the literature. Ultrasound measurement of cervical length is not recommended before 14 weeks’ gestation or after 35 weeks’ gestation.