Preterm birth (PTB) remains the major cause of neonatal morbidity and mortality. For the vast majority of spontaneous PTBs, the final pathway is opening of the cervix. Pessaries have been proposed since the 1950s as a possible intervention to keep the cervix closed and prevent spontaneous PTB (sPTB).1 They have the possible advantages of being noninvasive, relatively easy to place and to remove, and inexpensive (usually around $30–$40). But are pessaries safe and do they work for prevention of sPTB?
Types of pessaries
The pessary most studied for prevention of sPTB is the Arabin pessary (http://dr-arabin.de/arabin/e/cerclage.html). Dr Birgit Arabin’s father began to produce rubber pessaries in their garage in the 1950s in Germany. The Arabin pessary is the only such device whose safety and efficacy has been assessed in randomized controlled trials (RCTs).1-8
The Bioteque pessary (http://www.randjmedical.com/product/cup-pessary/), which is very similar, is available in the United States. It has been studied in 2 RCTs, the results of which will be presented at a meeting of the Society for Maternal-Fetal Medicine in January 2017.
How pessaries might work
The mechanism by which pessaries might work for preventing sPTB is unclear, but there are 2 leading hypotheses. One is that the pessary helps to keep the cervix closed. The other is that the pessary might direct the cervix more posteriorly and thus change the inclination of the cervical canal such that the weight is more directed to the anterior lower segment.1
How to place a pessary
Proper placement of a pessary for prevention of sPTB might seem easy but it is not if you have not been trained to do this procedure. A pessary is usually inserted with the woman in the lithotomy position. The device is bent and then inserted into the vaginal introitus with the small circle towards the patient. Then the operator’s fingers help gently place the pessary, which is now open in the vagina, snug against the fornices, and in particular, push the posterior caudal part of the device towards the posterior fornix.
The fingers should also ensure that the smaller circle of the pessary is around the cervix, with the external os palpable through the small pessary circle. Improper placement can cause a pessary to be ineffective, and maybe even harmful.
How to assess the cervix with a pessary in place
With a pessary in place, it is difficult to assess the cervix by either digital examination or by transvaginal ultrasound (TVU). Experts suggest leaving the device in place if at all possible, unless the membranes are ruptured, or significant cervical dilatation is expected.1
In cases of rupture of membranes (ROM), most experts recommend permanent removal of the device.1 While some clinicians have reported successfully imaging the cervix with a pessary in place, that is not easy to do.9
Use of pessaries for prevention of sPTB has been studied in thousands of patients.3-8 Although almost all of these patients experienced an increase in discharge, use of the devices in pregnancy has not been reported to be associated with serious maternal or perinatal complications.
In general, no reports exist of an association between pessary use and increased incidence of vaginal infections. In very rare cases, venous thromboembolism of the cervix, lacerations, strangulation of the cervix, fistulas, bleeding, urinary retention, and other complications have been reported.10
Evidence for efficacy
Several RCTs have evaluated the safety and efficacy of pessary use for prevention of sPTB. These trials have focused on 3 main populations: singletons with short TVU cervical length (CL); twins, unselected; and twins with short TVU CL (Table).
Singletons with short TVU CL
So far, 3 RCTs have been published in the literature on possible complications and effects of a pessary on singleton gestations in women with a short TVU CL.3-5 All used the Arabin pessary, and a short TVU CL ≤ 25 mm before 25 weeks’ gestation as criteria for inclusion. While the first published RCT from Spain showed significant benefits in terms of reduced PTB,3 the other 2 trials did not.4,5 It is unclear why results between studies differed, but some have postulated that better training of operators and, therefore, placement of the pessaries resulted in positive outcomes in 1 trial.
A meta-analysis of the 3 RCTs including 1420 women with a singleton gestation and a short TVU CL ≤ 25 mm before 25 weeks does not show any benefits in terms of PTB or neonatal outcomes of placing an Arabin pessary compared to no pessary (Table). Therefore the data so far do not uniformly support efficacy, hence pessaries should not be used routinely for prevention of PTB until more data become available.