Measurement error for ultrasound fetal biometry performed by paramedics in rural Bangladesh

To document the accuracy and precision of sonographic fetal biometry performed by nine paramedics from rural Bangladesh.

Paramedics underwent intensive training (6 weeks) including hands-on practice then underwent a series of standardization exercises. Measurements of each fetus were taken by a highly-trained medical doctor (study supervisor) and the nine paramedics. Crown-rump length (CRL) in fetuses of less than 10 weeks' gestation, and biparietal diameter (BPD), occipitofrontal diameter, head and abdominal circumference (AC) and femur diaphysis length (FL) were measured twice using standard procedures by each paramedic and the medical doctor for each fetus, with at least 20 min between them. Precision was quantified using variance components analysis; the intraobserver error for each of the paramedics was calculated by comparing repeat measurements taken on the same participant, and the measurements obtained by each individual paramedic were also compared with those taken by the others (interobserver error). Accuracy was estimated by comparing the mean of the two measures taken by each paramedic to those taken by the study supervisor using paired t-tests. Bland-Altman plots were used to visually assess the relationship between precision of repeat measurements (intraobserver error) and fetal size.

A total of 180 women, at 7 to 31 weeks' gestation, participated in the study. Intraobserver error of the measurements obtained by the paramedics, expressed as the mean SD, ranged from 0.97 mm for BPD in the first trimester to 7.25 mm for AC in the third trimester, and was larger than the interobserver error (i.e. accounting for a greater proportion of total variance) for most measurements. Interobserver error ranged from 0.00 mm for FL to 3.36 mm for AC, both in the third trimester. For all measurements except CRL, intraobserver error increased with increasing fetal size. The measurements obtained by the paramedics did show some statistically significant differences from those obtained by the study supervisor, but these were relatively small in magnitude.

Both inter- and intraobserver measurement errors were within the range reported in the literature for studies conducted by technical staff and medical doctors. With intense training, paramedics with no prior exposure to ultrasonography can provide accurate and precise measures of fetal biometry.