Reliability of ultrasound in the assessment of cervical incompetence

ABSTRACT

This study included 40 pregnant women with cervical incompetence and 60 women with normal pregnancy. In normal pregnancy the mean internal os diameter was 11.5 +/- 3.0 mm during the 1st trimester and 14.5 +/- 3.2 mm during the 2nd trimester. In women with cervical incompetence these measurements were 17.9 +/- 3.6 mm during the 1st trimester [P < 0.001] and 20.1 +/- 3.4 mm in the 2nd trimester [P-< 0.001]. When a cut-off point of 15 mm was used as a threshold for diagnosing the condition in the first trimester, it produced a sensitivity of 87.5% and a specificity of 86.7% with a false negative rate of 12.5% and a false positive rate of 13.3%. In the 2nd trimester a threshold of 20 mm produced a sensitivity of 50% and a specificity of 96.7% false negative rate 29.3% and 7.7% false postitive rate. These false rates were higher than could be acceptable as a screening test for cervical incompetence