Intraexaminer and interexaminer variability in 3D fetal volume measurements during the second and third trimesters of pregnancy.

Objective: To assess intra- and inter-examiner reliability of three dimensional fetal ultrasound measurements. Methods: Three dimensional (3D) fetal organ volumes (head, kidney, total thigh volume and fractional thigh volume (TVol)) were acquired during the second and third trimester, with the addition of placental volume in the second trimester, by 2 different experienced, blinded sonographers. 58 fetuses were examined from 21-39 weeks gestation. Intra and Inter-examiner reliability was assessed using Bland-Altman plots and their 95% limits of agreement, and intraclass correlation coefficients. Results: The most significant inter-examiner error was observed in second trimester kidney volume (95% limits of agreement ± 110%), and the best agreement was for third trimester TVol (95% limits of agreement ± 25%), and second trimester head volume (95% limits of agreement -7 to +25%). Second trimester and third trimester ICC results were all >0.75 apart from second trimester kidney volume intra (0.374) and inter-examiner (0.061) measurements, second trimester placenta inter-examiner measurements (0.390), and third trimester kidney inter-examiner measurements (0.647). Conclusions: 3D fetal ultrasound volumes of the head, kidney, total thigh and placenta have limited reproducibility and improvement in measurement techniques is needed before they can be used routinely to assess fetal growth. 3D TVol is reliably obtained in the late third trimester.