Emerging treatments

Cervical pessary in pregnant women with a short cervix

An Arabin® pessary is a flexible, ring-like silicone pessary, which has been suggested to reduce the preterm birth rate. One multicenter randomized control trial (RCT) assessed if the pessary conferred benefit in women with singleton pregnancies and a short cervix in comparison with progesterone, finding no decrease in preterm birth below 37 weeks’ gestation.[149]​ A 2022 Cochrane review found that the pessary may reduce the risk of delivery before 37 weeks (risk ratio [RR] 0.68, 95% CI 0.44 to 1.05) and 34 weeks (RR 0.72, 95% CI 0.33 to 1.55) in asymptomatic high risk women with singleton pregnancies compared with no treatment.[150]​ However, the evidence was low- to moderate-certainty and should be interpreted with caution due to statistical heterogeneity, imprecision, and risk of bias. Efficacy compared with progesterone was also uncertain, and there was little effect from the pessary with regards to maternal infection, neonatal unit admission, or neonatal mortality.[150]​ Studies found no benefit from the pessary for reducing preterm delivery rates in unselected twin pregnancies and in higher risk twin pregnancies with short cervix.[151][152]​​​ 

Progesterone therapies

Progesterone therapies reduce the incidence of preterm birth in women who have had a previous spontaneous preterm birth and in women who were incidentally found to have a short cervix.[84]​ In the US, the Food and Drug Administration (FDA) has withdrawn its approval for intramuscular hydroxyprogesterone as large commercial studies have not confirmed benefit. However, one meta-analysis suggests both vaginal and intramuscular preparations of progesterone may be beneficial in singleton pregnancies, with both reducing preterm delivery before 34 weeks gestation in high-risk singleton pregnancies (RR 0.78, 95% CI 0.68 to 0.90 and RR 0.83, 95% CI 0.68 to 1.01 respectively).[84]​ Although this meta-analysis did include women without a short cervix or other risk factors for preterm delivery, the numbers were small, and hence evidence is lacking to routinely offer women with no risk factors prophylactic progesterone. Evidence to support the use of oral preparations is lacking.[84]​ In multiple pregnancies, progesterone was not beneficial and may increase adverse effects.[84][85]​​​[86]​ The effect of progesterone on neonatal and maternal outcomes is less certain. Meta-analyses suggest consistently favorable neonatal outcomes but highlight the uncertainty of this effect.​[70][84]​​ Data is limited on the long-term effects of progesterone, but one systematic review reported no effects on children ages up to 8 years exposed to progesterone in utero, and a 4 year follow-up study showed no differences between 17-hydroxyprogesterone and placebo in any developmental outcomes assessed.[153][154]​​​ 

Use of this content is subject to our disclaimer