Quality of controlled clinical trials. The case of imaging ultrasound in obstetrics: a review.

Randomized controlled trials are increasingly used to assess clinical practices in obstetrics and gynaecology. The strength of these studies is that they usually address the issue of selection bias satisfactorily. Yet, as with any form of scientific investigation, the randomized controlled trial has inherent limitations and is subject to flaws in its conduct. Using basic methodological criteria, this report assesses the quality of the four published controlled trials in which a policy of routine imaging ultrasonography in pregnancy was compared with a more restrictive policy. In addition, a pooled analysis using data from all four trials was conducted to illustrate how increasing the sample size may reveal differences between the two policies which remain undetected in trials using small samples. The researchers in these studies reached different conclusions as to the effectiveness of routine ultrasound screening. Taken together, these four trials provide valuable information about routine ultrasound screening but fail to demonstrate adequately the usefulness of imaging ultrasound as a screening procedure for all pregnant women. The assessment criteria presented here could be used by investigators, editors, referees and other readers as a guideline for assessing the quality of therapeutic studies upon which clinical practice should be based.