Arabin cervical pessary in women at high risk of preterm birth: a magnetic resonance imaging observational follow‐up study

OBJECTIVE: To help elucidate the mechanism of action of the Arabin cervical pessary in pregnancies at high risk for preterm delivery. METHODS: Cervical length and uterocervical angle were evaluated in relation to gestational age in 198 pregnancies not at high risk for preterm birth that underwent clinical fetal magnetic resonance imaging (MRI). Additionally, in 73 singleton pregnancies at high risk for preterm birth, an Arabin cervical pessary was placed at 14-33 weeks' gestation. We performed MRI of the cervix immediately before and after placement and at monthly follow-up until removal of the pessary. In a subgroup of 54 pregnancies with a short cervix and pessary placement at 17-31 weeks' gestation, the uterocervical angle and cervical length at follow-up were compared with the preplacement values. RESULTS: In pregnancies not at high risk for preterm birth, the uterocervical angle did not vary, but cervical length showed a significant decrease with gestational age (r = -0.15, P 0.05). CONCLUSION: In patients at high risk for preterm delivery, correct placement of the Arabin cervical pessary should be checked immediately; this can be performed quickly and easily using MRI. This study provides some evidence that, in singleton pregnancies with a short cervix, a cervical pessary delays birth through a mechanical effect on the uterocervical angle.