South African Society for Ultrasound
in Obstetrics and Gynaecology


How long should an anomaly scan take?

by Dr John Parks
Consultant Obstetrician Gynecologist

Many ultrasound departments experience heavy scanning loads on a daily basis which they are expected to complete without missing any abnormalities.

It is not unusual for an ultrasound department in a busy hospital to get 50 to 100 cases in a morning. If there are limited numbers of ultrasonographers, they could individually scan up to 40 cases in the morning. Where this scenario exists, what is the risk of missing significant pathology due to inadequate visualization of all anatomic structures? Obviously this will depend on the expertise of the ultrasonographer.

In a survey from San Diego , * V Catanzarite and co-workers attempted to answer this question. They conducted 100 ultrasound examinations at 16 – 22 weeks gestational age. The scans performed attempted to complete a comprehensive survey of the fetus. If the scan lasted only 10 minutes, only 8% of all structures were visualized, 15 minute scans visualized 31%, 20 minutes – 53%, 25 minutes – 72% and 30 minutes – 81% of structures were visualized. Rates of completed anatomic surveys increased with advanced fetal age.

Obviously there are factors such as maternal weight, fetal position, abdominal wall scarring, amniotic fluid volume, gestational age and the quality of the ultrasound machine which, among others, will influence the time of scanning. The authors felt that 25 minutes is adequate in a normal patient. They also feel that 15 minutes is the minimum time that should be set for a scan.

In a litigation-dominated era of medical practice, it seems logical therefore to suggest that an attempt be made to allow sufficient time for our ultrasonographers to do their scanning properly.

* V Catanzarite et al. Ultrasound Obstet Gynecol 2005; 26: 521-526