What is preterm birth?
Preterm birth means birth before 37 weeks of pregnancy. It is the leading cause of death in newborn babies. Often, preterm birth is caused by weakness of the cervix (the lower, narrow end of the womb).
How can cervical weakness be treated to prevent preterm birth?
Methods used to treat cervical weakness include cervical cerclage (tightening the cervix with a stitch to prevent its premature opening), expectant management (monitoring without intervention until problems arise), medical treatment with the female sex hormone progesterone (administered vaginally) or a cervical pessary (a silicone ring used to close the cervix). The cervical pessary is inserted in the upper vagina at between 12 and 24 weeks of pregnancy and is removed at 37 weeks. It is a simple, minimally invasive procedure that does not require anaesthesia and may replace cervical cerclage.
What did we want to find out?
We wanted to find out if cervical pessary was better than any other treatment, or no treatment, for preventing preterm birth in women who were pregnant with a single baby (singleton pregnancy) and who were at risk of having cervical weakness.
What did we do?
We searched for studies that examined cervical pessary compared with any other treatment, or no treatment, in women with singleton pregnancy who were at risk of having cervical weakness. We compared and summarised the results of the studies and rated our confidence in the evidence, based on factors such as study methods and sizes.
What did we find?
We found eight randomised studies (where participants were randomly assigned to their treatment group) involving 2983 pregnant women. We were able to extract data for three comparisons: cervical pessary versus no treatment, cervical pessary versus progesterone, and cervical pessary versus cervical cerclage. The studies took place in 15 high-income countries.
In women with singleton pregnancy, the use of cervical pessary may decrease the risk of preterm birth compared to no treatment or vaginal progesterone, although the evidence around this was not robust. It is unclear if cervical pessary has an effect on maternal infection or other outcomes related to the baby for all comparisons.
What are the limitations of the evidence?
We have little confidence in the evidence because the results varied widely between studies and there were not enough studies. Future studies are needed to confirm the beneficial effect of cervical pessary on preterm birth. They should include lower-income settings so that the findings can be applied to a wider population.
How up to date is this evidence?
This evidence is up to date to September 2021.
In women with a singleton pregnancy, cervical pessary compared with no treatment or vaginal progesterone may reduce the risk of delivery before 34 weeks or 37 weeks, although these results should be viewed with caution due to uncertainty around the effect estimates. There is insufficient evidence with regard to the effect of cervical pessary compared with cervical cerclage on PTB.
Due to low certainty-evidence in many of the prespecified outcomes and non-reporting of several other outcomes of interest for this review, there is a need for further robust RCTs that use standardised terminology for maternal and offspring outcomes. Future trials should take place in a range of settings to improve generalisability of the evidence. Further research should concentrate on comparisons of cervical pessary versus cervical cerclage and bed rest. Investigation of different phenotypes of PTB may be relevant.
Preterm birth (PTB), defined as birth prior to 37 weeks of gestation, occurs in ten percent of all pregnancies. PTB is responsible for more than half of neonatal and infant mortalities and morbidities. Because cervical insufficiency is a common cause of PTB, one possible preventive strategy involves insertion of a cervical pessary to support the cervix. Several published studies have compared the use of pessary with different management options and obtained questionable results. This highlights the need for an up-to-date systematic review of the evidence.
To evaluate the benefits and harms of cervical pessary for preventing preterm birth in women with singleton pregnancies and risk factors for cervical insufficiency compared to no treatment, vaginal progesterone, cervical cerclage or bedrest.
We searched Cochrane Pregnancy and Childbirth’s Trials Register, ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform to 22 September 2021. We also searched the reference lists of included studies for additional records.
We included published and unpublished randomised controlled trials (RCTs) comparing cervical pessary with no treatment, vaginal progesterone, cervical cerclage or bedrest for preventing PTB. We excluded quasi-randomised trials. Our primary outcome was delivery before 34 weeks' gestation. Our secondary outcomes were 1. delivery before 37 weeks' gestation, 2. maternal mortality, 3. maternal infection or inflammation, 4. preterm prelabour rupture of membranes, 5. harm to woman from the intervention, 6. maternal medications, 7. discontinuation of the intervention, 8. maternal satisfaction, 9. neonatal/paediatric care unit admission, 10. fetal/infant mortality, 11. neonatal sepsis, 12. gestational age at birth, 13. harm to offspring from the intervention 14. birthweight, 15. early neurodevelopmental morbidity, 15. late neurodevelopmental morbidity, 16. gastrointestinal morbidity and 17. respiratory morbidity.
Two review authors independently assessed trials for eligibility and risk of bias, evaluated trustworthiness based on criteria developed by the Cochrane Pregnancy and Childbirth Review Group, extracted data, checked for accuracy and assessed certainty of evidence using the GRADE approach.
We included eight RCTs (2983 participants). We included five RCTs (1830 women) in the comparison cervical pessary versus no treatment, three RCTs (1126 pregnant women) in the comparison cervical pessary versus vaginal progesterone, and one study (13 participants) in the comparison cervical pessary versus cervical cerclage. Overall, the certainty of evidence was low to moderate due to inconsistency (statistical heterogeneity), imprecision (few events and wide 95% confidence intervals (CIs) consistent with possible benefit and harm), and risk of performance and detection bias.
Cervical pessary versus no treatment
Cervical pessary compared with no treatment may reduce the risk of delivery before 34 weeks (risk ratio (RR) 0.72, 95% CI 0.33 to 1.55; 5 studies, 1830 women; low-certainty evidence) or before 37 weeks (RR 0.68, 95% CI 0.44 to 1.05; 5 studies, 1830 women; low-certainty evidence). However, these results should be viewed with caution because the 95% CIs cross the line of no effect. Cervical pessary compared with no treatment probably has little or no effect on the risk of maternal infection or inflammation (RR 1.04, 95% CI 0.87 to 1.26; 2 studies, 1032 women; moderate-certainty evidence).
It is unclear if cervical pessary compared with no treatment has an effect on neonatal/paediatric care unit admission (RR 0.96, 95% CI 0.58 to 1.59; 3 studies, 1332 infants; low-certainty evidence) or fetal/neonatal mortality (RR 0.93, 95% CI 0.58 to 1.48; 5 studies, 1830 infants; low-certainty evidence) because the 95% CIs are compatible with a wide range of effects that encompass both appreciable benefit and harm.
Cervical pessary versus vaginal progesterone
Cervical pessary may reduce the risk of delivery before 34 weeks (RR 0.72, 95% CI 0.52 to 1.02; 3 studies, 1126 women; moderate-certainty evidence) or before 37 weeks (RR 0.89, 95% CI 0.73 to 1.09; 3 studies, 1126 women; moderate-certainty evidence), but we are uncertain of the results because the 95% CI crosses the line of no effect. The intervention probably has little or no effect on maternal infection or inflammation (RR 0.95, 95% CI 0.81 to 1.12; 2 studies, 265 women; moderate-certainty evidence).
It is unclear if cervical pessary compared with vaginal progesterone has an effect on the risk of neonatal/paediatric care unit admission (RR 0.98, 95% CI 0.49 to 1.98; low-certainty evidence) or fetal/neonatal mortality (RR 1.97, 95% CI 0.50 to 7.70; 2 studies; 265 infants; low-certainty evidence) because the 95% CIs are compatible with a wide range of effects that encompass both appreciable benefit and harm.
Cervical pessary versus cervical cerclage
Only one very small study of 13 pregnant women contributed data to this comparison; the results were unclear.