A comparison between ultrasonically assessed cervical volumes with modified bishop score to predict the favourability of the uterine cervix prior to induction of labour

Abstract

INTRODUCTION AND OBJECTIVES: Induction of labour (IOL) is one of the most frequently performed obstetric interventions. In current obstetric practice approximately 15-20% of women undergo induction of labour. Sri Lanka has the highest prevalence of IOL in the region (35%) according to WHO. Conventionally Bishop score system have been used to assess pre induction cervical favourability for vaginal delivery. Several recent studies have proposed that transvaginal sonographic assessment of cervical length is more sensitive in prediction of obstetric outcome in induction of labour. The purpose of this study was to comparatively assess the predictive value of ultrasonically assessed cervical volume, in compared to Modified Bishop’s score, prior to IOL. The primary objectives of the study were To compare the cervical volume with Modified Bishop Score for assessing the favorability of cervix prior to induction of labour. To evaluate the women’s perception on degree of discomfort caused by a transvaginal ultrasound scan at term. METHODS: Study was carried out as a cross sectional study. Pre induction digital cervical assessment and transvaginal two dimensional sonographic cervical volume assessment was done in 120 consecutive women admitted for IOL at term, by two different clinicians who were unaware of each other's findings. IOL was done according to a standard protocol, uniformly in all women. All the obstetric outcomes including induction delivery interval were documented.RESULTS: Out of 125 study participants 83(66.4%) were nulliparous and 42 (33.6%) were multiparous. The mean gestational age at induction of labour was 40 weeks. Vaginal delivery succeeded in 97 (77.6%) women and 28 (22.4%) of women needed caesarean section. In vaginal delivery group, in 65 (52%) women, delivery occurred within first twenty-four hours of primary modality of induction. In 56% of nulliparous women vaginal delivery occurred in first 24 hours compared to 85% of multiparous women. The median induction to delivery interval in multiparous women was 9 hours and in nulliparous women it is 19 hours. Induction success and likelihood of vaginal delivery within first 24 hours, increased with Bishop Score and decreased with cervical volume in a linear correlation. There was a significant association between induction to delivery interval (IDI) with the Bishop score and the cervical volume. Out of 125 study participants, 110 (88%) experienced minimal or no pain during procedure. 15 (12%) experienced moderate discomfort and no study participant report severe pain or discomfort.CONCLUSIONS: Transvaginal cervical volume assessment is comparable to Modified Bishop’s core, in predicting the likelihood of vaginal delivery within 24 h following IOL. It doesn’t cause significant discomfort to the pregnant women, when performed at term.