Reliability of fetal anthropometry by ultrasound

Abstract

The biparietal and abdominal diameters and cranial and abdominal perimeters of 14 [human] fetuses were measured a few hours before termination of pregnancy by elective cesarean section. The same measurements were made in the newborns. Each observer performed these measurements twice, ignoring the results of the other observers until the study was completed. Scannings were performed with a real-time ultrasound equipment, by an ultrasound expert and by a technician with 3 mo. training. The average values and standard deviation of the differences (.hivin.d, SD) of the measurements among observers and intra-observers, were established. The t-test for dependent samples was used to compare the results; the significant level was P < 0.05. No significant differences were found between the 1st and 2nd measurements of each observer, nor between ultrasound measurements obtained by the expert compared with those performed by the technician with 3 mo. training. When different techniques were used both observers showed a definite tendency to make larger measurements on the photograph. Regarding biparietal diameter, when comparing the frozen image measurement with real-time scanning, a significant difference was found in those performed by the more experienced observer, probably due to hazing of the contours when the freeze-frame is used. When comparing the 1st and 2nd measurement in newborns, no significant differences were found in the abdominal and cranial perimeters, nor in biparietal diameter. Ultrasound measurements of each observer compared with neonatal measurements showed no significant differences in biparietal diameter. Regarding cranial perimeter, both echographists made smaller measurements than the pediatrician, probably because in the photograph obtained by ultrasound the bone perimeter of the fetus is determined; in the newborn the thickness of the scalp is added. The abdominal diameter and perimeter are markedly different in the fetus and neonate, due to environmental changes occurring after birth.