Cervical Length Screening to Reduce Preterm Birth
Vaginal progesterone was also associated in this trial with a 38% reduction in spontaneous preterm birth before 35 weeks’ gestation, and a 50% reduction before 28 weeks’ gestation. In addition, there was a significantly lower incidence of respiratory distress syndrome (RDS) and a lower rate of any neonatal morbidity or mortality in the vaginal progesterone group (Ultrasound Obstet. Gynecol. 2011;38:18-31).
The publication this year of an individual patient data meta-analysis of randomized controlled trials in asymptomatic women with a midtrimester cervical length of 25 mm or less provides added evidence of progesterone’s benefit (Am. J. Obstet. Gynecol. 2012;206:124.e1-19).
The meta-analysis by Dr. Roberto Romero and colleagues covered 775 women (723 singleton pregnancies) with a sonographic short cervix of 25 mm or less in the midtrimester. Overall, treatment with vaginal progesterone was associated with a 42% reduction in the rate of preterm birth at less than 33 weeks’ gestation. Women with singleton gestation and no prior preterm birth had a 40% reduction, and women with a singleton gestation and at least one prior preterm birth had a 46% reduction.
Treatment with vaginal progesterone also was associated in singletons with significant reductions in the rate of preterm birth at less than 35 weeks’ and less than 28 weeks’ gestation, the incidence of RDS, composite neonatal morbidity and mortality, birth weight, and NICU admission.
A beneficial role of pessary use in women with midtrimester short cervical length is also emerging, with benefits seen in the PECEP trial (Lancet 2012;379:1800-6).
Ready for Screening
In the past 3 years, at least several articles advocating universal cervical length screening and vaginal progesterone – and at least two cost-effectiveness analyses supporting such calls – have been published. One, by a team at Yale University, for instance, calculated significant cost-savings and numbers of neonatal deaths and long-term neurologic deficits that would be prevented with universal screening in low-risk pregnancies (Ultrasound Obstet. Gynecol. 2011;38:32-7).
Unfortunately, however, the use of transvaginal ultrasound cervical length screening in singleton gestations without a history of spontaneous preterm birth continues to be a controversial issue.
In a committee opinion on "Incidentally Detected Short Cervical Length" issued in April this year, the American College of Obstetricians and Gynecologists (ACOG) recommended that a cervical length measurement be performed at the time the ultrasound examination is undertaken for fetal anatomic survey at around 18-22 weeks’ gestation, and said "cervical length measured by transvaginal ultrasound examination is a useful screening test for predicting spontaneous preterm birth."
Interestingly, the ACOG opinion was withdrawn shortly after publication and the college issued a Practice Bulletin in October 2012 on "Prediction and Prevention of Preterm Birth." The bulletin reaffirms that "cervical length screening by transvaginal ultrasonography is safe, highly reproducible, and more predictive than transabdominal ultrasound screening" and digital examination.
Despite such conclusions, however, ACOG fell short of mandating routine transvaginal cervical length screening in women without prior preterm birth. The bulletin states instead that "this screening strategy may be considered" and that "practitioners who decide to implement universal cervical length screening should follow one of the protocols for transvaginal measurement of cervical length from the clinical trials" (Obstet. Gynecol. 2012;120:964-73).
There are no recommendations regarding specific management options or strategies for short cervix detected by transabdominal ultrasound or other methods, possibly because published studies have involved diagnoses confirmed by transvaginal ultrasound. It seems fair, therefore, to assume that if a short cervix is detected by any other method, transvaginal ultrasound will need to be performed for accuracy and to determine the prognosis and management plan.
The Society for Maternal-Fetal Medicine also recognized in a recently published guideline that universal cervical screening in singleton pregnancies without prior preterm birth is a "reasonable" option – one that can be considered by individual practitioners but "cannot be mandated" (Am. J. Obstet. Gynecol. 2012;206:376-86).
The SMFM guideline takes a more decisive stance with respect to singletons with prior preterm birth, recommending transvaginal ultrasound cervical length measurements every 2 weeks and providing management decisions for those who choose to offer universal screening in all singleton gestations. All told, the language suggests to me that SMFM is encouraging universal screening without mandating it.
Critics of universal screening have cited a concern that facilities for transvaginal ultrasound screening are not widely enough available. Others have spoken about an uncertainty that screening outcomes in actual practice will compare favorably with the outcomes of controlled trials. There also is concern about the potential misuse or overuse of technology, and concern that many women will undergo treatment unnecessarily.
