Fundal height measurement: Part 5—The effect of clinician bias on fundal height measurements

Abstract

The purpose of this study was to determine whether clinicians' fundal height measurements were influenced by their ability to see the numeric markings on the tape measure during the measurement procedure, and by their knowledge of gestational weeks. Ten certified nurse-midwives and four student nurse-midwives each obtained measurements from 24 women. Each clinician obtained two fundal height measurements with unmarked paper tape measures and two fundal height measurements with marked paper tape measures. The fundal height measurement obtained and recorded on the prenatal chart by the clinician responsible for the woman's routine prenatal visit at the time of data collection was also recorded by the researchers. Comparison of the differences between the clinician's two marked and two unmarked tape measurements demonstrated that the differences between the two marked tape measurements were smaller (mean absolute difference = 0.61 cm) than the differences between the two unmarked tape measurements (mean absolute difference = 0.97 cm). When the gestational weeks were compared with the unmarked and marked tape measurements and with the fundal height measurements recorded on the prenatal record, the smallest differences were between the fundal height measurements recorded on the prenatal record and gestational weeks (mean absolute difference = 1.51 cm); the next smallest differences were between the marked tape measurements and gestational weeks (mean absolute difference = 1.89 cm); and the largest differences were between the unmarked tape measurements and gestational weeks (mean absolute difference = 2.15 cm). These findings demonstrate that clinicians' fundal height measurements are biased by their ability to see the numeric markings on the tape measure and by their knowledge of gestational weeks. These findings suggest that clinicians should blind themselves to their own fundal height measurements and to the number of gestational weeks to avoid the effects of clinician bias on their fundal height measurements.