These sections briefly explain why the committee made the recommendations and how they might affect practice. They link to details of the evidence and a full description of the committee's discussion.
There was good evidence that vaginal progesterone reduced the risk of preterm birth before 34 weeks in women with a previous history of preterm birth, and in women with a short cervix (25 mm or less). The committee were aware that these groups overlapped, as some women with a previous history of preterm birth will also have a short cervix. Therefore, they adopted the recommendation from the previous guideline to offer vaginal progesterone to women with a previous history of preterm birth and a short cervix. The committee concluded that, as in the previous guideline, progesterone should be offered as an equal option with cervical cerclage (for which no new evidence review had been conducted), as there is no evidence to determine which of these options is more effective.
As the treatment options are very different (regular use of vaginal progesterone pessaries throughout pregnancy, compared with a single operative procedure), the committee highlighted that the choice of treatment should be made after discussion of the risks and benefits of the 2 treatments.
The committee were aware that there is uncertainty regarding which risk factors should be used to identify women at risk of preterm birth (cervical length measurements, previous history of preterm birth, previous cervical surgery). There is also variation in practice across the country regarding which women are offered cervical length scanning. Cervical scanning is currently offered when there is clinical concern regarding the risk of preterm birth, rather than as a routine part of antenatal care. Also, vaginal progesterone may be effective at reducing preterm birth for women with some risk factors, but not others.
Identifying specific groups of women who would benefit from treatment with progesterone was difficult because of the overlap in risk factors for an individual woman: some women with a previous history of preterm birth also have a cervical length of 25 mm or less, and some women with a cervical length of 25 mm or less also have a previous history of preterm birth. Therefore, it was hard to determine which of these 2 factors could identify women at high risk of preterm birth who would definitely benefit from treatment with vaginal progesterone. Consequently, the committee agreed that treatment with progesterone should be considered for women with either of these risk factors (cervical length of 25 mm or less, or a previous history of preterm birth). Because of the uncertainty over the benefits of progesterone in women who have risk factors for a preterm birth but do not have a cervical length of 25 mm or less, and women who have a cervical length of 25 mm or less but do not have a history of preterm birth, the committee made research recommendations on this topic.
The timing of progesterone administration varied between the studies. However, most trials started treatment between 16+0 and 24+0 weeks. This was in keeping with the experience of the committee members, therefore they made a recommendation to start treatment at any suitable time during that range of gestational age. There was no evidence on when progesterone should be stopped, but the committee's experience was that it should be continued until at least 34 weeks. As there was uncertainty about these timings, the committee also made a research recommendation on the optimal timing of treatment.
The recommendation on ensuring a plan is in place for removal of the suture when prophylactic cervical cerclage is used was made in response to an NHS England safety report, which highlighted some instances when removal did not happen.
Vaginal progesterone is a relatively inexpensive and commonly used treatment for women at risk of preterm birth, so the recommendations are unlikely to significantly alter practice. As vaginal progesterone should now be considered for women with a history of preterm birth (with an unknown cervical length or a cervical length greater than 25 mm on scan), this might increase the use of progesterone, but the benefits of reduced numbers of preterm births are likely to lead to cost savings overall.
The recommendation on planning for removal of the suture when prophylactic cervical cerclage is used is not expected to affect practice.
Full details of the evidence and the committee's discussion are in evidence review A: clinical effectiveness of prophylactic progesterone in preventing preterm labour.
The recommendation on ensuring a plan is in place for removal of the suture when 'rescue' cervical cerclage is used was made in response to an NHS England safety report, which highlighted some instances when removal did not happen.
The recommendation is not expected to affect practice.