Pitfalls in sonographic imaging of the incompetent uterine cervix.

Artifacts interfering with sonographic imaging of the uterine cervix in pregnancy are described. Increasing the amount of fluid in the urinary bladder closes the cervix and alters the configuration of the lower uterine segment, while increased intra-uterine pressure results in reciprocal changes. Angulation of the transducer and manual pressure thereon distort sonographic findings. It is concluded that, contrary to recent reports in the literature, sonography cannot reliably demonstrate changes in cervical compliance during pregnancy. Vaginal examination remains the ultimate diagnostic modality for the diagnosis of the incompetent cervix, while sonography may be used as an adjunct only.