The importance of quality management in fetal measurement

Objectives The aims of this study were to evaluate factors contributing to inaccuracy in fetal measurements and to assess the clinical importance of measurement quality. Methods One hundred images of biparietal diameter (BPD), head circumference (HC) and abdominal circumference (AC) measurements were collected from six centers (1800 measurements); the proportion meeting quality criteria was assessed. Four hundred images of AC were collected from one center, each image measured by ellipse fitting and tracing methods; clinical agreement between the methods was assessed. Fetal weight estimation (EFW) errors were compared between quality controlled and non-quality controlled studies. Images of three ACs on each of 400 fetuses were collected; where one measurement failed to meet quality criteria, it was compared with an optimal measurement on the same fetus. Results Eighty-nine percent, 87% and 60% of BPD, HC and A C, respectively, met all quality criteria. Limits of agreement between ellipse and traced AC were -4.7 mm to 12.5 mm; 22% of sections were non-elliptical. EFW errors were significantly different but were confounded by differences in time to delivery. Limits of agreement between optimal and suboptimal AC measurements were -15.1 mm to 7.7 mm. Conclusions AC quality criteria are less easily recognized and obtained than those for head measurements; training, adherence to protocols and audit are important. Differences between ellipse and traced A C may not justify the use of separate charts; the number of non-elliptical sections suggests that ellipse fitting is not appropriate. Comparison between EFW errors is not a suitable tool for audit. Failure to meet quality criteria results in clinically significant errors.