OC09.02: Should cervical length be assessed by transabdominal or transvaginal ultrasound during pregnancy?

Abstract

Objectives: There is no consensus on the best approach to cervical surveillance during pregnancy: should all women have a transvaginal (TV) scan or can this be restricted to women with a short cervix on initial transabdominal (TA) assessment? This study compares TA and TV assessment of cervical length at 16–41 weeks gestation. Methods: TA and TV ultrasound measurements of cervical length were made at 16–41 weeks gestation. Cervical length was measured from internal to external os using the landmarks described by the FMF. Bland-Altman plots and paired t-tests were used to look at differences in TA and TV measurement. The screening efficacy of initial TA assessment in defining a group for TV evaluation is also reported. Results: 367 women participated including 273, 84 and 10 presenting at 16–23, 24–35 and >36 weeks respectively. Overall, the TA method underestimated cervical length by 2.5 mm (95% CI 1.7–3.4 mm). Bland Altman plots showed an inverse trend with shorter cervixes after 24 weeks. 17 women had a cervix 36 weeks. The sensitivity and specificity of TA assessment of cervical length at 24–36 weeks gestation were 1/10 (0.10) and 70/74 (0.95) respectively; positive and negative predictive values were 1/5 (0.20) and 70/79 (0.89). At >36 weeks the sensitivity was 0/6 (0.0) and the specificity was 2/4 (0.5). Conclusions: TA measurements do not reflect TV assessment accurately, particularly if the cervix is short ( 24 weeks gestation. There is no value in TA assessment of the cervix >36 weeks.