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Cervical assessment at the routine 23-weeks' scan: problems with transabdominal sonography
1Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London, UK.
Summary
Transabdominal sonography is less reliable for measuring cervical length in pregnancy compared to transvaginal methods. Transabdominal scans often fail to visualize the cervix, especially short ones, and can provide inaccurate longer measurements with a full bladder.
Area of Science:
- Obstetrics and Gynecology
- Medical Imaging
- Perinatology
Background:
- Cervical length assessment during pregnancy is crucial for identifying preterm delivery risk.
- Transvaginal sonography is the established method for accurate cervical length measurement.
Purpose of the Study:
- To compare transabdominal and transvaginal sonographic cervical length measurements.
- To identify factors influencing transabdominal visualization and measurement accuracy.
Main Methods:
- 149 pregnant women at 23 weeks gestation underwent both transabdominal and transvaginal sonography.
- Cervical length was measured transvaginally with an empty bladder.
- Transabdominal visualization and measurement were assessed against bladder volume, BMI, and cervical length.
Main Results:
- Transvaginal sonography successfully visualized the cervix in all cases.
- Transabdominal visualization improved with increased bladder volume (42% to 73%) and longer cervical lengths (13% to 51%).
- Transabdominal measurements were significantly longer with a full bladder compared to an empty bladder.
Conclusions:
- Transabdominal sonography is unreliable for identifying women at risk of preterm delivery due to poor visualization rates, particularly for short cervices.
- Transvaginal sonography remains the preferred method for accurate cervical length assessment.
- Full bladder technique for transabdominal scans leads to falsely increased cervical length measurements.