Identification and Validation of ultrasound parameters to predict birthweight and identify late-onset fetal growth restriction

Abstract

Background: Single estimates of fetal size are poor at detecting growth restricted infants, especially in the late third trimester. Current guidelines recommend comparing EFW on scans to fetal intra-uterine birth weight charts generated from cross-sectional studies that do not account for each individual fetuses growth potential. Individualised growth assessment (IGA) methods using 3D ultrasound provide a means for evaluating true growth restriction which may result in earlier detection of fetal growth abnormalities. Hypothesis, Aims and Objectives: We tested the hypothesis that ultrasound parameters obtained longitudinally through the second and third trimesters can be used to assess fetal growth and identify fetuses deviating from their early pregnancy growth trajectory. Methods: New Ultrasound Parameters in Pregnancy (NUPS) is a prospective, longitudinal cohort study of an unselected normal pregnancy population. Measurements of 2D and 3D fetal size parameters, as well as fetal Doppler measurements were obtained at scan intervals of 6-8 weeks from 14 weeks gestation until 36 weeks gestation. Automated volume measurements were obtained using 4Dview software (GE Healthcare). Individualised growth assessment (IGA) using the iGAP software (http://iGAP.research.bcm.edu) was used to predict third trimester growth trajectories and birthweight. Additionally, multiple linear regression analysis and multi-level mixed effects model were used to identify predictors of birthweight at different scan intervals. Repeatability was assessed using intraclass correlation coefficients (ICC) and Bland-Altman Plots. Results: 3D fractional thigh volume has low measurement error and ICC values in the third trimester of 0.943-0.992. There was a modest improvement in the detection of both SGA and FGR using TVol derived measures compared to standard 2D measurements at 34-36 weeks (AUC= 0.86 (95% CI 0.79-0.94,), and 0.92 (95% CI 0.85-0.99), respectively. IGA using the iGAP online computer program can be used reliably to identify growth restricted fetuses that are deviating from their third trimester growth trajectories. Both gestational age and the presence of SGA (EFW < 10th centile)/FGR (EFW < 3rd centile) independently affect uterine artery pulsatility index (UtA-PI) values and the effect of SGA/FGR over time appears to be constant. Discussion: This series of studies demonstrates that enhanced detection of late-onset FGR is possible and there is potential with individualised growth assessment methods to improve perinatal outcomes.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Edward Johnstone (Supervisor) & Jenny Myers (Supervisor)