Transabdominal cervical length measurement as primary screening method for short cervix in the mid-trimester: A...

Preterm birth (PTB) is a leading cause of neonatal morbidity and mortality, with cervical insufficiency being a major contributor. While transvaginal ultrasound is the gold standard, concerns over invasiveness, resource requirements, and acceptability limit its universal use. Transabdominal cervical length measurement may offer a pragmatic alternative, particularly in conservative populations. We aim to compare transabdominal versus transvaginal cervical length measurement for screening of short cervix during the mid-trimester, and to determine the feasibility and clinical utility of using transabdominal ultrasound as a primary screening tool, especially in populations with reservations about undergoing transvaginal scans.

This was a prospective observational cohort diagnostic accuracy study involving pregnant women undergoing routine mid-trimester anomaly scans. Cervical length was measured using transabdominal and transvaginal ultrasound by experienced sonographers.

correlation assessed with Spearman's coefficient. Agreement evaluated with intraclass correlation and Bland-Altman plots. Diagnostic accuracy metrics (sensitivity, specificity, PPV and NPV) were calculated for transabdominal thresholds. Confounding factors, including bladder filling, maternal body mass index (BMI), and prior caesarean delivery on visualisation, were also evaluated.

Of the 266 women eligible to participate in the study, 6.0% were excluded as they declined a transvaginal scan. Postvoid transabdominal (TA) measurements demonstrated better agreement with transvaginal (TV) values but were associated with higher rate of nonvisualization (10.0%). Bland-Altman plots showed good agreement without systematic bias. The mean prevoid TA cervical length and postvoid TA cervical length were 35.7 mm and 35.6 mm respectively, compared to 39.3 mm on TV measurement. Non-visualization occurred more often postvoid (10%) than prevoid (6.4%), while postvoid TA measurements showed stronger agreement with TV (ICC=0.818). Agreement of measurements was higher among Maternal-Fetal Medicine (MFM) consultants than among MFM fellows. Body mass index (BMI) and prior caesarean section scars did not significantly affected visualization or measurement accuracy.

TA cervical length measurement is a reliable initial screening approach for identifying women at risk of short cervix during mid-trimester when performed by experienced operators. It serves as a pragmatic alternative in settings where TV scans are declined or not feasible, facilitating timely referral for TV confirmation and early initiation of preventive interventions such as progesterone therapy or cerclage. However, its application may be limited in untrained hands.