Randomised Placebo Controlled Trial of Outpatient Cervical Ripening with Isosorbide Mononitrate

BMC Pregnancy and Childbirth 2006, 6:25 doi:10.1186/1471-2393-6-25
An Open Access research article from BMC

Abstract (provisional) Study protocol

Background
There is increasing interest in carrying out pre-induction cervical ripening on an outpatient basis. However, there are concerns about the use of prostaglandins, the agents commonly used in hospital settings for this indication, because prostaglandins induce uterine contractions that may lead to fetal hypoxia. Indeed, in a recent study we demonstrated abnormalities in 9% of fetal heart rate tracings performed following prostaglandin induced cervical ripening at term. In contrast, we confirmed in the same study that isosorbide mononitrate (administered on an inpatient basis) was both effective in inducing cervical ripening at term, and was associated with no associated fetal heart rate abnormalities. Methods / design The aim of this study is to determine whether isosorbide mononitrate self administered by women on an outpatient basis improves the process of induction of labour. Specifically, we hypothesise that the use of outpatient IMN will result in a shorter inpatient stay before delivery, decreased costs to the health service and greater maternal satisfaction with ripening and induction of labour, compared with placebo treatment. In the study described here (the IMOP study), women scheduled for induction of labour at term, and who require pre-induction cervical ripening will be randomised to self-administer at home either isosorbide mononitrate 40mg, or a placebo, each vaginally, at 48 hours, 32 hours and 16 hours before scheduled hospital admission. After admission to hospital, treatment will revert to the usual induction of labour protocol. We will compare the primary outcomes of the elapsed time interval from hospital admission to vaginal delivery, the costs to the health service of induction of labour, and women's experience of induction of labour in the two groups.

Discussion
This trial will provide evidence on the efficacy of outpatient isosorbide mononitrate for pre-induction cervical ripening at term. We will study a formulation of isosorbide mononitrate which is cheap and widely available. If the treatment is effective, acceptable to women, and cost effective, it could be implemented into obstetric practice worldwide. Trial registration The trial has been registered on the International Standard Randomised Controlled Trial Number Register (ISRCTN) and given the registration number ISRTN39772441.

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