Vaginal progesterone

Progesterone is a natural sex steroid produced in pregnancy by the corpus luteum and subsequently the placenta. It plays a key role in maintenance of pregnancy in the first trimester and blocking pro­gesterone receptors (e.g.

Short cervix with no prior history of PTB

Fonseca et al. performed an RCT on 250 women of 200 mg nightly vaginal progesterone versus placebo started at 24 weeks in women with a short cervix (CL PPROM, chorioamnionitis, cervical trauma, suture displacement and bleeding. The reported rate of chorioamnionitis after HIC is 6.2%, while PPROM ranges from 18% to 38% (57). Therefore, it is im­portant to weigh up individual risks and benefits prior to suture placement.

History-indicated cervical cerclage

Cervical cerclage can be placed because of a prior history of PTB or a previous history of failed elective cervical cerclage (HIC). A history- indicated cerclage is usually placed at 12-13 weeks of pregnancy, once a successful first trimester is completed. The evidence for history-indicated cerclage is much weaker than ultrasound- indicated cerclage and is entirely based on a subgroup analysis of an RCT including just 107 women which showed a decrease in PTB before 33 weeks in women with three or more prior PTB or second- trimester miscarriages (58).

Ultrasound-indicated cerclage-prior preterm birth

In a meta-analysis of five trials of 504 women who were random­ized to cerclage placement if they had a previous history of PTB and CL less than 25 mm, before 24 weeks of gestation, PTB less than 37 weeks decreased by 30% and perinatal morbidity and mortality by 36% after cerclage placement (59). However, a Cochrane review of 12 trials involving 3328 women at high risk for PTB showed no stat­istically significant difference in perinatal deaths despite a similar significant reduction in PTB (average RR 0.80; 95% CI 0.69-0.95; nine trials, 2898 women) (60).

Ultrasound-indicated cerclage-no prior preterm births

In a low-risk singleton population, treatment with a cervical cerc­lage for a short CL between 16 and 24 weeks has not been shown in any single individual trial (61, 62) to be of benefit in reducing rates of PTB at less than 35 weeks.

Physical exam-indicated cerclage/rescue cerclage

A cerclage placed when (usually) symptomatic women are found to have significant cervical dilatation, detected on vaginal examination, performed either digitally or with a speculum. The evidence remains weak for this practice and there are no long-term safety data to ad­dress the effects of keeping a baby to develop in a potentially inflam­matory or infected environment. There is only one trial including 23 participants of physical exam-indicated cerclage plus indomethacin versus bed rest alone (63) which drew the conclusion that physical exam-indicated cerclage, indomethacin, antibiotics, and bed rest Transabdominal cerclage

Vaginal placement of a cervical cerclage has a lower rate of ma­ternal morbidity than placing a cerclage at the level of the internal os through the abdominal route. It is generally reserved for women who have failed a previous vaginal cerclage. A transabdominal cerc­lage can be sited via (a) open surgery or (b) laparoscopic surgery. Open surgery is performed through a Pfannenstiel incision to the lower abdomen. Currently there are no published RCTs of women receiving abdominal suture but a multicentre randomized trial of high versus low versus abdominal cerclage in women with a pre­vious failed elective stitch shows that transabdominal cerclage is far superior to a repeat vaginal suture (MAVRIC) (64).

Cerclage material

Ongoing clinical trials are looking at the effect of the type of suture used on reduction of PTB rates and particularly infection. Evidence of significant alteration of the vaginal microbiome using a braided suture or tape when compared to a monofilament suggests that monofilament may be better to prevent ascending bacterial infec­tion.

Arabin pessary

Pessaries have been used for centuries for the treatment of genital organ prolapse. In 1959, their use was documented in a small case series of women with cervical incompetence or uterus didelphys to take pressure away from the internal cervical os. In the late 1970s, Hans Arabin in West Germany designed a round cone-shaped pes­sary made of flexible silicone. Its dome-like design resembled the vaginal fornix, with the aim of surrounding the cervix as closely as possible to the internal os. The mechanism of action of the pessary is not completely clear. It has been suggested that after insertion it increases the uterocervical angle, removing direct pressure of the fetal head onto the cervix (65). TVUS images of its use are shown in Figure 30.4.

The first randomized trial included 385 women with a CL not greater than 25 mm, and compared Arabin pessary to expectant management. Only 11% of women had previously had a PTB. Spontaneous delivery at less than 34 weeks was significantly less fre­quent in the pessary group (6%) than the expectant group (27%) (OR 0.18; 95% CI 0.08-0.37) (66). The second trial with the same design was unfortunately underpowered as the rate of short cervix in the screened population was too low (5%) and only recruited 108 women with no significant effect (PTB or to standard treatment (72). Although the pessary did not reduce PTB or the primary neonatal composite outcome overall, both were significantly reduced in the prespecified subgroup of women with a CL less than the 25th centile (n = 143) with a RR of PTB before 32 weeks of 0.49 (95% CI 0.24-0.97) and RR of composite neonatal outcome of 0.42 (95% CI 0.19-0.91). Another study (73) randomized 1180 women at a later stage in pregnancy (20-24⁺⁶) to Arabin pessary or no intervention, again there was no significant difference in the rate of sPTB at less than 34 weeks (13.6% vs 12.9%; RR 1.1; 95% CI 0.8-1.4) and a post hoc subgroup analysis of 214 women with a CL less than or equal to 25 mm showed no benefit of insertion of the pessary. The distinct difference between these two trials was the mean gestation at which the Arabin was sited; there is a suggestion that intervention at later gestations may be too late to prevent sPTB. Currently a United Kingdom-led trial, STOPPIT 2, is ongoing to assess the benefit of Arabin pessary in a twin pregnancy population with a short cervix.