The benefits, costs of universal cervical length screening

Screening certainties and doubts

In 2011, my colleagues and I compared the cost effectiveness of two approaches to preterm birth prevention in low-risk pregnancies: no screening versus a single transvaginal ultrasound cervical-length measurement in all asymptomatic, low-risk singleton pregnant individuals between 18 and 24 weeks’ gestation.

In our model, women identified as having a cervical length less than 1.5 cm would be offered vaginal progesterone. Based on published data, we assumed there would be a 92% adherence rate, and a 45% reduction in deliveries before 34 weeks with progesterone treatment.

We found that in low-risk pregnancies, universal transvaginal cervical-length ultrasound screening and progesterone intervention would be cost effective and in many cases cost saving. We estimated that screening would prevent 248 early preterm births – as well as 22 neonatal deaths or neonates with long-term neurologic deficits – per 100,000 deliveries.

Our sensitivity analyses showed that screening remained cost saving under a range of clinical scenarios, including varied preterm birth rates and predictive values of a shortened cervix. Screening was not cost saving, but remained cost effective, when the expense of a transvaginal ultrasound scan exceeds $187 or when vaginal progesterone is assumed to reduce the risk of early preterm delivery by less than 20% (Ultrasound Obstet. Gynecol. 2011;38;32-37).

Neither the American College of Obstetricians and Gynecologists nor the Society for Maternal-Fetal Medicine support mandated universal transvaginal ultrasound cervical length screening. Both organizations state, however, that the approach may be considered in women with singleton gestations without prior spontaneous preterm birth.

Interestingly, Thomas Jefferson University in Philadelphia, which uses a universal screening program for singleton gestations without prior preterm birth, has recently published data that complicate the growing trend toward universal cervical length screening.

The Philadelphia clinicians followed a strategy whereby women with a transvaginal cervical length of 2 cm or less were prescribed vaginal progesterone (90 mg vaginal progesterone gel, or 200 mg micronized progesterone gel capsules). Those with a cervical length between approximately 2 cm and 2.5 cm were asked to return for a follow-up cervical length measurement before 24 weeks’ gestation.

What they found in this cohort was surprising: a rate of short cervix that is significantly lower than what previous research has shown.

Among those screened, 0.8% of women had a cervical length of 2 cm or less on an initial transvaginal ultrasonogram. Previously, a prevalence of 1%-2% for an even shorter cervical length (less than 1.5 cm) was fairly consistent in the literature.

As Dr. Kelly M. Orzechowski and her colleagues point out, the low incidence of short cervix “raises questions regarding whether universal transvaginal ultrasonogram cervical length screening in low-risk asymptomatic women is beneficial” (Obstet. Gynecol. 2014;124:520-5).

In our 2011 cost-effectiveness analysis, we found that screening was no longer a cost-saving practice when the incidence of cervical length less than 1.5 cm falls below 0.8%. Screening remained cost effective, however.

Recently, we found that if the Philadelphia protocol is followed and the U.S. population has an incidence of shortened cervix similar to that described by Dr. Orzechowski and her colleagues, universal cervical length screening in low-risk singleton pregnancies is cost effective but not cost saving. Furthermore, we found several additional plausible situations in this unpublished analysis in which universal screening ceased to be cost effective.

Thus, before we move to a strategy of mandated universal screening, we need better population-based estimates of the incidence of short cervix in a truly low-risk population.

We also must consider the future costs of progesterone. It is possible that costs may increase significantly if vaginal progesterone wins approval from the Food and Drug Administration for this indication.

Finally, if universal cervical length screening is to become the standard of care, we need policies in place to prevent misuse of the screening technology that would inevitably drive up costs without improving outcomes. For example, we must ensure that one cervical length measurement does not transition into serial cervical length measurements over the course of pregnancy, since measurement after 24 weeks has limited clinical utility. Similarly, progesterone use for a cervical length less than or equal to 2.0 cm cannot progress to progesterone for anyone approaching 2.0 cm (i.e. 2.5 cm or even 3 cm) as there is no evidence to suggest a benefit for women with longer cervixes.

Over time, it would be beneficial to have additional data on how best to manage patients who have a cervical length of 2 cm-2.5 cm before 24 weeks’ gestation. Many of us ask these women to return for a follow-up measurement and some may prescribe progesterone. However, we lack evidence for either approach; while a cervical length measurement less than 2.5 cm is clearly associated with an increased risk of preterm birth, the benefit of treatment has been demonstrated only with a cervical length of 2 cm or less.