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

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-amenorrahea 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 an ideal cut-off of 33mm. For post-void TAS the shortest length was 28mm 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 favorable for TAS.