Preterm birth (PTB) remains an outcome with no current effective prevention in twin pregnancies, but this meta-analysis by Schuit et al. and other data suggest that better times are coming. Cerclage, progesterone, bed rest, uterine activity monitoring, and prophylactic tocolysis have thus far been shown to be associated with no decrease in PTB when given to twins without any other specific risk factor for PTB.
Cervical length measured by transvaginal ultrasound (TVU CL) is one of the most effective screening tests for singleton gestations. The Society for Maternal–Fetal Medicine (SMFM) and the American College of Obstetricians and Gynecologists (ACOG) have published clinical guidelines for singleton pregnancies stating that: ‘implementation of such a screening strategy can be viewed as reasonable, and can be considered by individual practitioners, following strict guidelines' (SMFM, Berghella V. Am J Obstet Gynecol 2012;206:376–86; ACOG Obstet Gynecol 2012;120:964–73). This is based on two bodies of literature. First, if a TVU CL of ≤20 mm is identified before 25 weeks of gestation in singleton pregnancies without prior spontaneous PTB, vaginal progesterone has been proven beneficial in two randomised controlled trials (RCTs) including over 700 women. Second, if a TVU CL of <25 mm is identified before 24 weeks of gestation in singleton pregnancies with prior spontaneous PTB, ultrasound-indicated cerclage has been found to be beneficial in a meta-analysis of five RCTs including over 500 women (Berghella et al. Obstet Gynecol 2011;117:663–71). As can be seen, it took several RCTs specifically designed to address the effect of either vaginal progesterone or cerclage in singleton pregnancies with a short TVU CL, and several hundreds of randomised patients, to show these significant effects.
Although TVU CL is also predictive of PTB in twin gestations, so far no intervention has been definitively shown to be helpful in preventing PTB, and its consequences, in multiple gestations with short CL. Cerclage has been evaluated in twins with a short CL, and is not only not useful, but may indeed be harmful; however, this has been evaluated in RCTs with just 49 sets of twins with TVU CL <25 mm before 24 weeks of gestation (Berghella et al. Obstet Gynecol 2005;106:181–9), and thus deserves further study. Recently, the use of a vaginal pessary has been associated with significant reductions in PTB of <28 and <32 weeks of gestation, as well as composite poor perinatal outcome, in a secondary analysis of an RCT including 133 twins with a TVU CL<38 mm before 23 weeks of gest-ation (Liem et al. Lancet 2013;382:1341–9).
In this meta-analysis by Schuit et al., 17–alpha-hydroxy progesterone caproate was not found to be beneficial in reducing PTB or adverse perinatal outcome in 175 twin pregnancies (with >90% of mothers with no prior spontaneous PTB) with a TVU CL ≤25 mm before 24 weeks of gestation (Table S3). Vaginal progesterone was also found not to be beneficial in preventing PTB at <34 weeks of gestation in 58 twin pregnancies (with >95% of mothers with no prior spontaneous PTB) with a TVU CL ≤25 mm before 24 weeks of gestation, but was associated with a significant 43% decrease in adverse perinatal outcome (Table S4).
Interestingly, another meta-analysis (which did not report the details of the data from each RCT included) also reported no prevention of PTB, but did report a decrease in composite neonatal morbidity and mortality in 51 twin pregnancies with a TVU CL ≤25 mm in the second trimester (Romero et al. Am J Obstet Gynecol 2012;206:124.e1–19). The trends in both of these meta-analyses showed a decrease in PTB, which might not have been significant because of the small numbers included in the studies (type–II error).
So, what is the clinician to do in 2014? For now, the evidence is still limited to start screening all twins with TVU CL to try to prevent PTB. But the future looks bright. If large, well-designed RCTs (several of which are currently in progress) confirm the possible benefits of pessary and/or vaginal progesterone in twins with a short TVU CL before 24 weeks of gestation, then TVU CL could become an effective screening strategy for this population.
Disclosure of interest
Nothing to disclose.