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James Mulhearn MAppSc

North Coast X-Ray & Imaging, Ormuz Avenue, Caloundra Qld 4551

In 1997, an audit of a major district hospital was undertaken to quantify the effectiveness of obstetric ultrasound examinations. The main objective was to determine the sonographic accuracy of second and third trimester obstetric examinations performed by the hospital. The methods, outcomes and recommendations have been summarised in the following paper.

Introduction
A congenital anomaly is defined as an anatomical or structural abnormality present at birth. Congenital anomalies are responsible for 20% to 30% of perinatal deaths and an even higher percentage of perinatal morbidity¹. Because most anomalies occur randomly in fetuses without any known risk factors, routine sonography as a screening tool is now considered an important component of pregnancy management by most clinicians. It has been estimated that in most Western countries, such as Australia, Great Britain, North America and Western Europe, as many as 80% of women seeking obstetric care will now have at least one ultrasound examination during their pregnancy².

As improvements in technology and experience have been made, so too have the goals of antenatal ultrasound changed. Whereas antenatal ultrasound was once considered to be only a relatively reliable means of determining the number, position and age of fetuses, it is now used to provide a reasonably extensive morphological examination and assessment of the apparent normality of the unborn fetus. One of the most critical factors in the antenatal assessment of fetal structural anomalies is the accuracy of the ultrasound diagnosis. Inaccurate diagnoses may result in incorrect reassurance to parents regarding fetal normality and possibly inadequate preparation for post-delivery complications. Alternatively, concerns and alterations to pregnancy management may occur, such as subjection to tertiary referral, invasive diagnostic testing, or genetic counseling. Additionally, failure to diagnose significant anomalies may increase medico-legal liability³.

It has been suggested that each institution performing antenatal ultrasound examinations should know their own level of sensitivity for congenital anomaly detection in low-risk populations4. In ideal circumstances there would be detailed follow-up, by post-natal study, on all fetal ultrasound examinations performed to determine the accuracy of the antenatal diagnoses3. To achieve a 'gold standard', studies such as these would be required to obtain complete ascertainment of each newborn for malformations, especially those which may not always be apparent at birth such as congenital heart and renal defects. Complete ascertainment would have to include postnatal imaging studies of all the organs studied antenatally, clearly an impractical goal, since the great majority of newborns enter and continue in the world as healthy individuals. A more achievable but still acceptable objective is to compare antenatal ultrasound records to clinical findings documented at birth and then to determine the percentage of structural malformations clinically present at birth which were identified by antenatal ultrasound.

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