Objective: Induction of labor for medical indications has become a routine practice. To date, the Bishop score remains as the standard method to predict the duration of induced labor. Elastography is an objective method of assessing the relative consistency of tissues. Therefore, we sought to assess strain elastography of cervix to predict delay from induction to delivery in pregnant women with a low Bishop score.
Patients and methods: Ultrasound elastography was immediately performed before induction of labor for medical indications among patients with a singleton pregnancy at>36 weeks of gestation and a Bishop score<6. Patients received 50 μg of misoprostol intravaginally, repeated 6 hours later if regular painful uterine contractions had not started. A second ultrasound elastography was also performed 6 hours after starting the induction before the second dose of misoprostol if regular painful uterine contractions had not started. At each examination, a color map from blue (hardest tissue) to red (softest tissue) was produced. The cervical elastography was considered as positive if at least one part of its anterior wall was red. We assessed the predictive value of elastography on vaginal delivery within 24 hours. Patients delivering by cesarean section were excluded from this study.
Results: Elastography was initially performed in 48 patients. Twelve patients delivering by cesarean section after induction of labor were excluded, leading to 36 patients evaluated in this study. Among these 36 patients with elastography performed before induction of labor, 20 had a second elastography before the second dose of misoprostol. Sensibility, specificity, positive predictive value (PPV) and negative predictive value (NPV) of elastography performed before induction of labor on vaginal delivery within 24 hours were 40%, 27.3%, 55.6%, and 16.7%, respectively. Sensibility, specificity, PPV and NPV of elastography performed before the second dose of misoprostol were 64.3%, 16.7%, 64.3% and 16.7%, respectively. Among the 8 patients with red color occurring on the second cervical color map, sensibility, specificity, PPV and NPV were 83.3%, 0%, 62.5%, and 0%.
Discussion and conclusion: Qualitative cervical elastography is a poor predictor for delay from induction to delivery in pregnant women with a low Bishop score.
Keywords: Cervix; Col utérin; Consistance; Consistency; Déclenchement; Elastography; Induction of labor; Élastographie.
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