These findings prompted a reassessment by Berghella and coworkers (201r1), who performed a metaanalysis using individual patient data (Fig. 42-7). he primary outcomes from the included trials did not support cerclage placement. However, these investigators concluded that cerclage signiicantly prevented preterm birth and improved composite perinatal mortality and morbidity in women with prior spontaneous preterm birth, singleton gestation, and cervical length <25 mm.
One caveat in the interpretation of this cerclage data is the inluence of obstetrical history. For example, all of the trials comprising the metaanalysis included preterm birth as early as 16 to 17 weeks' gestation. Deining these early second trimester losses as preterm births, rather than cervical incompetence, is problematic. Thus, it is diicult to distinguish whether these women were treated in the context of cervical incompetence or of preterm labor at 16 weeks. Nonetheless, based on these
Risk Ratio StudyorSubgroup M-H, Fixed, 95% CI 0.01 0.1 10 100
FIGURE 42-7 Cerclage versus no cerclage for prevention of recur rent preterm birth in women with a cervical length <25 mm. Forest plot analysis of composite perinatal mortality and morbidity. CI = confidence index. (Adapted with permission from Berghella V, Rafael TJ, Szychowski JM, et al: Cerclage for short cervix on ultrasonography in women with singleton gestations and previous preterm birth: a meta-analysis, Obstet Gynecol 117(3):663,2011.) indings, the American College of Obstetricians and Gynecologists (2016c) concluded that in women with a singleton pregnancy, prior spontaneous preterm birth before 34 weeks, cervical length <25 mm, and gestational age <24 weeks, cerclage placement may be considered.
• Prophylaxis with Progestogen Compounds
In most mammals, progesterone withdrawal is considered to be a parturition-triggering event. During human parturition, however, maternal, fetal, and amnionic fluid progesterone levels remain elevated. It has been proposed that human parturition involves functional progesterone withdrawal mediated by decreased activity of progesterone receptors (Chap. 21, p. 401). It follows conceptually that the administration of progesterone may block preterm labor. This hypothesis has stimulated several studies of both 17 -alpha hydroxyprogesterone caproate (17OHP-C) and vaginally administered progesterone in women with varying risks for preterm birth.
At present, the reported benefits of either of these progestogen therapies are limited to women with singleton pregnancies. Progesterone prophylaxis speciically in multifetal gestations has not lowered preterm birth rates (Caritis, 2009; Rouse, 2007). Accordingly, both the American College of Obstetricians and Gynecologists (2016c) and the Society for Maternal-Fetal Medicine (2017 a) approve the use of progestogen therapy for prevention of preterm birth in select women with singleton pregnancies. Criteria are a history of prior preterm birth or no prior preterm birth but a sonographically identified short cervix.
17 -OHP-C is a synthetic progestogen, and the first and only drug approved by the FDA for prevention of recurrent preterm birth. The approval in 2011 was supported by a study by the Maternal-Fetal Medicine Units (MFNIU) Network (Meis, 2003). In this trial, 463 women with a prior preterm birth were randomly assigned to receive weekly intramuscular injections of inert oil or 17-0HP-C from 16 through 36 weeks' gestation. They reported a significantly reduced recurrence of preterm birth in 36 percent of women receiving 17-0HP-C compared with 55 percent of those given placebo.