Progesterone and cerclage together for short cervix: evaluating potential complementary effects for improved preterm birth prevention.

Management of patients with a short cervical length (CL) on transvaginal ultrasound (TVU) often involves therapy with vaginal progesterone and/or cervical cerclage. Although these interventions are frequently viewed as alternative strategies, they may also represent complementary approaches targeting different mechanisms involved in spontaneous preterm birth. As in other areas of medicine, therapies with different mechanisms are often used together rather than as mutually exclusive options. In line with current level 1 evidence from randomized controlled trials (RCTs) and meta-analyses of RCTs on either vaginal progesterone or cerclage, in singleton gestations with no prior spontaneous preterm birth (SPTB), vaginal progesterone is recommended when a TVU CL≤25 mm before 24 weeks is identified; if progressive cervical shortening occurs (eg, CL≤20 mm before 24 weeks), UIC may be considered and continuation of vaginal progesterone may be considered. Similarly, in singleton gestations with prior SPTB, vaginal progesterone is typically initiated at 16 weeks, and if a short cervix (TVU CL<25 mm before 24 weeks) develops, UIC is recommended, continuation of vaginal progesterone may also be considered. In addition, there are limited but growing data that vaginal progesterone and cerclage used together for a short TVU CL before 24 weeks have potential complementary effects, with decreased incidence of PTB compared to using either vaginal progesterone alone, or cerclage alone. Overall, the available evidence on the combined use of progesterone and cerclage remains limited, with relatively few studies, most of which are observational, retrospective and of modest methodological quality; therefore, more research is needed. International guidelines should address the use of this combined approach of both vaginal progesterone and cerclage for a short mid-trimester TVU CL.