Objective
To compare third trimester size trajectory prediction errors for
three individualized fetal growth assessment methods.
Methods
This study utilized longitudinal measurements of 9 directly measured
size parameters in 118 fetuses with normal neonatal growth outcomes.
Expected Value [EV] function coefficients and variance components were
obtained using two-level random coefficient modeling. Growth models [IGA] or
EV coefficients and variance components [PLM, CPM] were used to calculate
predicted values at approximately 400 3rd trimester time points.
Percent Deviations [% Dev] calculated at these time points were
expressed as percentages of their IGA, age-specific reference ranges
(T%Dev). Third trimester T%Dev values were averaged
[aT%Dev] for each parameter. Means ± SD’s for sets
of aT%Dev values derived from each method [IGA, PLM, CPM] were
calculated and compared.
Results
Mean aT%Dev values for nine parameters were: 1) IGA:
– 4.3 to 5.2% [9/9 not different from zero]; 2) PLM:
−32.7% to 25.6% [4/9 not different from zero]; and
3) CPM: −20.4% to 17.4% [5/9 not different from
zero]. Seven of nine systematic deviations from zero were statistically
significant when IGA values were compared to either PLM or CPM values.
Variabilities were smaller for IGA when compared to those for PLM or CPM,
with 1) 5/9 being statistically significant [IGA vs. PLM], 2) 2/9 being
statistically significant [IGA vs. CPM] and 3) 5/9 being statistically
significant [PLM vs. CPM].
Conclusions
Significant differences in the agreement between predicted third
trimester size parameters and their measured values were found for the three
methods tested. With most parameters, IGA gave smaller mean aT%Dev
values and smaller variabilities. The CPM method was better than PLM
approach for most but not all parameters. These results suggest that
3rd trimester size trajectories are best characterized by IGA
in fetuses with normal growth outcomes.