[False diagnosis in prenatal sonography - analysis of causes and formulation of conclusions for the quality management of prenatal sonographic diagnostics]

Abstract

Aim: Aim of this study, carried out in a single third level gynaecological centre, was a detailed analysis of all cases with foetal anomalies not detected prior to 24th gestational week. Based on our results, we wanted to work out recommendations towards improving quality in prenatal ultrasound in Switzerland.

Methods: Retrospective survey (by means of our clinical database and a questionnaire) including all foetuses and neonates with morphological or functional anomalies which had been scanned in the Prenatal Ultrasound Unit of the University Hospital of Zurich in the year 2001.

Results: 50,8 % of the 185 cases were detected prior to 24 weeks, 36,2 % in the third trimester and 13 % after delivery. 26,0 % were classified as "missed, although detectable prior to 24 weeks" (group A) and 23,2 % of the cases as "not detectable prior to 24 weeks" (group B). A great majority of the missed cases were cardiac malformations and skeletal anomalies. As primary causes for the missed cases doctors mentioned unfavourable position, oligohydramnios and multiple pregnancies. Scanning at gestational stages not recommended in the screening time-table as well as not following a checklist was responsible for 20 % of all missed diagnoses, whereas ultrasound equipment was not a major problem.

Conclusions: The current 11-14 weeks' and 20-23 weeks' scan in Switzerland allows, at best, a 75-80 % detection rate of congenital anomalies prior to 24 weeks. Some 20 - 25 % of abnormalities appear as late as the last trimester, the majority being urogenital malformations. Roughly one third of early detectable malformations are currently missed, heart defects and skeletal anomalies being the leading causes. The detection rate could be improved by strictly following the Swiss guidelines.