Evaluation of cervical length by transabdominal and transvaginal scans during early pregnancy.

Abstract

Objective: To compare the measurements and the client-preferences of transabdominal scan (TAS) and transvaginal scan (TVS) in assessing cervical length.Method: A validation study with a cross sectional component on patient-preferences was conducted among 568 pregnant women with a period-of-amenorrhoea between 11+0 to 22+6 weeks. Pre-and post-void TAS and a post-void TVS measurements were taken. Receiver Operating Characteristics (ROC) curves were generated to assess the detection of short cervix using pre and post void TAS at different lengths of the cervix. Results:The mean (SD) age of the participants was 28.4 (5.7) years with a mean gestation age of 14+1 weeks. The mean (SD) cervical lengths detected by the pre-void TAS, post-void TAS and TVS were 32.2 (5.8) mm, 28.9 (5.8) mm and 34.4 (5.3) mm respectively. Factors with significant association with a higher TVS cervical length were; increasing age (p<0.001), higher gravidity (p<0.001), higher parity (p<0.001) and higher number of vaginal deliveries (p<0.001). The TAS and TVS measurements significantly correlated with each other (p<0.001).Post-void TAS could not obtain measurement in 49.47% of attempts. The shortest cervical length can be detected by pre-void TAS was 26mm with a ideal cut-off of 33 mm. For post-void TAS the shortest length was 28 mm with an ideal cut-off of 28.16mm. Majority preferred TAS over TVS. Conclusion:Pre-void TAS can predict a cervical length of 26mm or less with 87.5% sensitivity whereas the shortest length predicted by post-void is relatively longer. Nearly in half, a valid post-void TAS could not be recorded. Client preference was more favourable for TAS.