Is it possible to identify factors which affect the efficacy of screening for congenital malformations by ultrasonography?

Abstract

Purpose: To assess whether the efficacy of second-trimester ultrasound screening for fetal malformations is affected by patient-, staff-, team- or work environment-related factors. Methods and design: Prospective cohort study in a Danish University hospital in 1997 and 1998. Participants: A number of 7845 pregnant women who had an ultrasound screening in weeks 18–20. Ultrasound examinations were performed abdominally by eight nurses with special training in obstetrical ultrasonography. The ultrasonographers were divided into three groups according to their experience at the start of the study. Data: A record of all malformations diagnosed by ultrasound was entered into a database. Data included the name, date of birth, body mass index of the pregnant woman, date and time of the ultrasound scan, number of persons performing the scan, name of the first and last examiner, their charge and level of expertise, number of fetuses, gestational age, structural malformation diagnosed, information about amniocentesis, date of delivery, sex of the child(ren), malformation(s) diagnosed at delivery or autopsy. Follow-up of the children was done by searching their files and by a cross-check with the diagnostic registries of the two pediatric departments in the city of Copenhagen. The length of follow-up was between 12 and 36 months. The ability to detect significant malformations on ultrasound was related to: 1 factors related to the patient (body mass index, number of fetuses, gestational age at time of screening); 2 factors related to the staff (experience of sonographer); 3 factors related to the team (number of sonographers); 4 factors related to the work environment (weekday, time of day, number of scans, work monotony, number of ultrasound screenings for malformations, and work load in the ultrasound department). Results: Significant malformations were found in 106 fetuses, when followed up at least until 1 year of age, corresponding to an incidence of 1.3%. The overall detection rate was 65.1% as 69 malformations were detected and 37 were not. No case of neural tube defect, diaphragmatic hernia, gastroschisis or omphalocele was missed. Six out of seven cases of hydrocephalus were detected, while two cases of microcephaly were not. Regarding the severe heart malformations, one out of four cases of hypoplastic left heart was detected. High maternal body mass index was associated with a lower detection rate, while the presence of twins or the gestational age at the time of screening was not. There was no correlation between the sonographer's level of experience and the detection rate. Fetuses with an undetected malformation were significantly more often scanned by more than one sonographer than fetuses without malformations. There was a trend towards a lower detection rate on Thursdays, at mid-day, when most of the staff was at work, and when the number of malformation screenings exceeded 20 per day. Conclusions: In our center, 65% of significant malformations were diagnosed, a detection rate comparable to other centers, especially since we followed the children until the age of 1 year. The detection rate of fetal heart malformations was however, low, and therefore a course with special focus on this organ was offered to the sonographers. Our study demonstrates that among the patient-related factors high maternal body mass index was the only factor associated with a lower detection rate. Among the team-related factors, malformed fetuses were significantly more often examined by two sonographers than fetuses without congenital malformations. As to the factors related to the work environment, scans performed just before lunchtime or on days when most sonographers were at work seemed to have a lower detection rate. In order to minimize error, the following changes have been made: Appointments for screening were reorganized so they are not scheduled around mid-day. A morning- and a lunch-break without any planned examinations have been scheduled in order to allow all the staff to be together at some time during the day. When an experienced sonographer requests a second opinion, a doctor should give this. The new organization will be followed up in order to secure that the reorganization has not created new organizational mistakes.